crush after a couple minutes of working

I open it and start working. Everything seems fine but after a couple minutes (and some times less) it crashes. It happens only if I really work - if it just stays opened and I do nothing then nothing happens. I tried purge & update & upgrade & reboot & install. I've recently upgraded from Ubuntu 16.04 to 18.04 and haven't used pinta scince the upgrade, so it can be something with it. After the crush I get this in the terminal:

$ pinta
free(): invalid pointer
Stacktrace:

  at <unknown> <0xffffffff>
  at (wrapper managed-to-native) GLib.SList.g_free (intptr) <0x0005f>
  at GLib.ListBase.Empty () <0x0013c>
  at GLib.ListBase.Dispose (bool) <0x0000f>
  at GLib.ListBase.Finalize () <0x0001d>
  at (wrapper runtime-invoke) object.runtime_invoke_virtual_void__this__ (object,intptr,intptr,intptr) <0x00068>

Native stacktrace:

 /usr/bin/mono(+0xc8514) [0x557d86293514]
 /lib/x86_64-linux-gnu/libpthread.so.0(+0x12890) [0x7ff9a8cd2890]
 /lib/x86_64-linux-gnu/libc.so.6(gsignal+0xc7) [0x7ff9a86f5e97]
 /lib/x86_64-linux-gnu/libc.so.6(abort+0x141) [0x7ff9a86f7801]
 /lib/x86_64-linux-gnu/libc.so.6(+0x89897) [0x7ff9a8740897]
 /lib/x86_64-linux-gnu/libc.so.6(+0x9090a) [0x7ff9a874790a]
 /lib/x86_64-linux-gnu/libc.so.6(cfree+0x4cc) [0x7ff9a874ee1c]
 [0x41dd4e70]

Debug info from gdb:

[New LWP 13616]
[New LWP 13617]
[New LWP 13618]
[New LWP 13619]
[New LWP 13620]
[New LWP 13625]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x00007ff9a87cbbf9 in __GI___poll (fds=0x557d890fb190, nfds=3, timeout=500) at ../sysdeps/unix/sysv/linux/poll.c:29
29 ../sysdeps/unix/sysv/linux/poll.c: No such file or directory.
  Id Target Id Frame
* 1 Thread 0x7ff9a987b780 (LWP 13615) "Main" 0x00007ff9a87cbbf9 in __GI___poll (fds=0x557d890fb190, nfds=3, timeout=500) at ../sysdeps/unix/sysv/linux/poll.c:29
  2 Thread 0x7ff9a7bff700 (LWP 13616) "SGen worker" 0x00007ff9a8ccd9f3 in futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x557d86786a08) at ../sysdeps/unix/sysv/linux/futex-internal.h:88
  3 Thread 0x7ff9a82a6700 (LWP 13617) "Finalizer" 0x00007ff9a8cd223a in __waitpid (pid=13628, stat_loc=0x7ff9a82a476c, options=0) at ../sysdeps/unix/sysv/linux/waitpid.c:30
  4 Thread 0x7ff99732b700 (LWP 13618) "dconf worker" 0x00007ff9a87cbbf9 in __GI___poll (fds=0x557d8896b530, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
  5 Thread 0x7ff996b2a700 (LWP 13619) "gmain" 0x00007ff9a87cbbf9 in __GI___poll (fds=0x7ff9900074c0, nfds=2, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
  6 Thread 0x7ff996329700 (LWP 13620) "gdbus" 0x00007ff9a87cbbf9 in __GI___poll (fds=0x7ff99000c0c0, nfds=3, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
  7 Thread 0x7ff97e68e700 (LWP 13625) "pool" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38

Thread 7 (Thread 0x7ff97e68e700 (LWP 13625)):
#0 0x00007ff9a87d2839 in syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
#1 0x00007ff99e88689a in g_cond_wait_until () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007ff99e813571 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#3 0x00007ff99e813b2c in g_async_queue_timeout_pop () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#4 0x00007ff99e868c3e in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#5 0x00007ff99e868195 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#6 0x00007ff9a8cc76db in start_thread (arg=0x7ff97e68e700) at pthread_create.c:463
#7 0x00007ff9a87d888f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 6 (Thread 0x7ff996329700 (LWP 13620)):
#0 0x00007ff9a87cbbf9 in __GI___poll (fds=0x7ff99000c0c0, nfds=3, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1 0x00007ff99e8405c9 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007ff99e840962 in g_main_loop_run () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#3 0x00007ff99f2910e6 in () at /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0
#4 0x00007ff99e868195 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#5 0x00007ff9a8cc76db in start_thread (arg=0x7ff996329700) at pthread_create.c:463
#6 0x00007ff9a87d888f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 5 (Thread 0x7ff996b2a700 (LWP 13619)):
#0 0x00007ff9a87cbbf9 in __GI___poll (fds=0x7ff9900074c0, nfds=2, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1 0x00007ff99e8405c9 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007ff99e8406dc in g_main_context_iteration () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#3 0x00007ff99e840721 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#4 0x00007ff99e868195 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#5 0x00007ff9a8cc76db in start_thread (arg=0x7ff996b2a700) at pthread_create.c:463
#6 0x00007ff9a87d888f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 4 (Thread 0x7ff99732b700 (LWP 13618)):
#0 0x00007ff9a87cbbf9 in __GI___poll (fds=0x557d8896b530, nfds=1, timeout=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1 0x00007ff99e8405c9 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007ff99e8406dc in g_main_context_iteration () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#3 0x00007ff99733336d in () at /usr/lib/x86_64-linux-gnu/gio/modules/libdconfsettings.so
#4 0x00007ff99e868195 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#5 0x00007ff9a8cc76db in start_thread (arg=0x7ff99732b700) at pthread_create.c:463
#6 0x00007ff9a87d888f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 3 (Thread 0x7ff9a82a6700 (LWP 13617)):
#0 0x00007ff9a8cd223a in __waitpid (pid=13628, stat_loc=0x7ff9a82a476c, options=0) at ../sysdeps/unix/sysv/linux/waitpid.c:30
#1 0x0000557d862935f0 in ()
#2 0x00007ff9a8cd2890 in <signal handler called> () at /lib/x86_64-linux-gnu/libpthread.so.0
#3 0x00007ff9a86f5e97 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#4 0x00007ff9a86f7801 in __GI_abort () at abort.c:79
#5 0x00007ff9a8740897 in __libc_message (action=action@entry=do_abort, fmt=fmt@entry=0x7ff9a886db9a "%s\n") at ../sysdeps/posix/libc_fatal.c:181
#6 0x00007ff9a874790a in malloc_printerr (str=str@entry=0x7ff9a886bd88 "free(): invalid pointer") at malloc.c:5350
#7 0x00007ff9a874ee1c in _int_free (have_lock=0, p=0x557d88fa41a0, av=0x7ff9a8aa2c40 <main_arena>) at malloc.c:4157
#8 0x00007ff9a874ee1c in __GI___libc_free (mem=0x557d88fa41b0) at malloc.c:3124
#9 0x0000000041dd4e70 in ()
#10 0x0000557d88fa41b0 in ()
#11 0x0000557d886770d0 in ()
#12 0x0000557d886770d0 in ()
#13 0x0000000000000000 in ()

Thread 2 (Thread 0x7ff9a7bff700 (LWP 13616)):
#0 0x00007ff9a8ccd9f3 in futex_wait_cancelable (private=<optimized out>, expected=0, futex_word=0x557d86786a08) at ../sysdeps/unix/sysv/linux/futex-internal.h:88
#1 0x00007ff9a8ccd9f3 in __pthread_cond_wait_common (abstime=0x0, mutex=0x557d86786a20, cond=0x557d867869e0) at pthread_cond_wait.c:502
#2 0x00007ff9a8ccd9f3 in __pthread_cond_wait (cond=0x557d867869e0, mutex=0x557d86786a20) at pthread_cond_wait.c:655
#3 0x0000557d8641b863 in ()
#4 0x00007ff9a8cc76db in start_thread (arg=0x7ff9a7bff700) at pthread_create.c:463
#5 0x00007ff9a87d888f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 1 (Thread 0x7ff9a987b780 (LWP 13615)):
#0 0x00007ff9a87cbbf9 in __GI___poll (fds=0x557d890fb190, nfds=3, timeout=500) at ../sysdeps/unix/sysv/linux/poll.c:29
#1 0x00007ff99e8405c9 in () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#2 0x00007ff99e840962 in g_main_loop_run () at /usr/lib/x86_64-linux-gnu/libglib-2.0.so.0
#3 0x00007ff9a4a9da37 in gtk_main () at /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0
#4 0x0000000041dbebea in ()
#5 0x00007ffdc4dc6a60 in ()
#6 0x00007ffdc4dc6a50 in ()
#7 0x00007ff9a7c00950 in ()
#8 0x00007ff9a7c00d60 in ()
#9 0x00007ff9a7c00db0 in ()
#10 0x0000557d886a9370 in ()
#11 0x0000000041c996d0 in ()
#12 0x00007ffdc4dc65e0 in ()
#13 0x00007ffdc4dc6490 in ()
#14 0x0000000041dbeb7c in ()
#15 0x00007ffdc4dc65e0 in ()
#16 0x0000000041c99688 in ()
#17 0x00007ff9a7c021f0 in ()
#18 0x00007ff9a7c00788 in ()
#19 0x00007ff9a7c021f0 in ()
#20 0x00007ff9a9774130 in ()
#21 0x00007ff9a7c00788 in ()
#22 0x00007ff9a7c021f0 in ()
#23 0x00007ff9a9770130 in ()
#24 0x00007ff9a7c00788 in ()
#25 0x00007ff9a7c021f0 in ()
#26 0x00007ff9a9768130 in ()
#27 0x00007ff9a7c00400 in ()
#28 0x0000000000000000 in ()

=================================================================
Got a SIGABRT while executing native code. This usually indicates
a fatal error in the mono runtime or one of the native libraries
used by your application.
=================================================================

Aborted (core dumped)