/usr/bin/update-manager:5:g_settings_schema_get_value:g_settings_schema_key_init:g_settings_get_value:g_settings_get_int:ffi_call_SYSV

Here's part of the stacktrace:

#0 _g_log_abort (breakpoint=1) at ../../../../glib/gmessages.c:583
        debugger_present = 1
#1 0xb74c68cf in g_log_default_handler (log_domain=0xb73aa9b8 "GLib-GIO", log_level=6, message=0x8877e10 "Settings schema 'com.ubuntu.update-manager' does not contain a key named 'launch-count'", unused_data=0x0) at ../../../../glib/gmessages.c:3158
        fields = {{key = 0xb7513b9c "GLIB_OLD_LOG_API", value = 0xb75686e2, length = -1}, {key = 0xb7513ace "MESSAGE", value = 0x8877e10, length = -1}, {key = 0xb7513ae1 "PRIORITY", value = 0xb7513991, length = -1}, {key = 0xb7513b3b "GLIB_DOMAIN", value = 0xb73aa9b8, length = -1}}
        n_fields = <optimized out>
#2 0xb74c6b77 in g_logv (log_domain=0xb73aa9b8 "GLib-GIO", log_level=G_LOG_LEVEL_ERROR, format=0xb73d929c "Settings schema '%s' does not contain a key named '%s'", args=0xbf8217dc "P\024\226\b\360\246\226\b\360\246\226\b\260\030\202\277\300:\272\267\254\207\357\267\360\251h\b\231\310\071\267\034@G\267\360\246\226\b\254\030\202\277x\030\202\277\005\320\071\267\030\373\225\b\360\246\226\b\244DD\265<\030\202\277\030\373\225\b") at ../../../../glib/gmessages.c:1370
        domain = 0x0
        data = 0x0
        depth = 1
        log_func = 0xb74c6810 <g_log_default_handler>
        domain_fatal_mask = <optimized out>
        masquerade_fatal = 0
        test_level = 6
        was_fatal = 0
        was_recursion = 0
        buffer = <optimized out>
        msg = 0x8877e10 "Settings schema 'com.ubuntu.update-manager' does not contain a key named 'launch-count'"
        msg_alloc = 0x8877e10 "Settings schema 'com.ubuntu.update-manager' does not contain a key named 'launch-count'"
        i = 2
        size = <optimized out>

This is related to the following change:

revno: 2829 [merge]
author: Andrea Azzarone <email address hidden>
committer: Sebastien Bacher <email address hidden>
branch nick: update-manager
timestamp: Thu 2018-09-06 00:02:30 +0200
message:
  Add a reminder to enable Livepatch (LP: #1787553).

It's not an issue with the code but glib aborting on a missing schemas key (which is considered as a corrupted installation), the reasons can include
- the schemas update failed
- there is a local installation taking over the system schemas and outdated/not providing the key
- could be that the program get started before the schemas cache has been updated (by its trigger), that's not likely though

It's not really easy to tell what's going on without having a reporter who hit the issue to provide details