Comment 8 for bug 1847275

I have the same problem on two Ubuntu 18.04 hosts.
The error does not occur immediately. Sometimes it takes several days.

Reboot (systemctl restart stunnel4.service) helps.

stunnel.log: INTERNAL ERROR: Bad magic at ssl.c, line 117

# stunnel4 -v
[ ] Clients allowed=500
[.] stunnel 5.44 on x86_64-pc-linux-gnu platform
[.] Compiled with OpenSSL 1.1.0g 2 Nov 2017
[.] Running with OpenSSL 1.1.1 11 Sep 2018
[.] Update OpenSSL shared libraries or rebuild stunnel
[.] Threading:PTHREAD Sockets:POLL,IPv6,SYSTEMD TLS:ENGINE,FIPS,OCSP,PSK,SNI Auth:LIBWRAP
[ ] errno: (*__errno_location ())
[!] Invalid configuration file name "-v"
[!] realpath: No such file or directory (2)