Comment 21 for bug 1847275

I made a more radical decision, I upgraded to 20.04 LTS (focal), installed Stunnel 5.56 and so far I have not had any crashes.
For those who want and can do this upgrade, I recommend them, since not only is Stunnel updated, but also OpenSSL.
For newbies like me I share the commands:

sudo apt update
sudo apt upgrade
sudo do-release-upgrade -d

After that the Stunnel looks like this:

root@ip-xxxxx:/home/ubuntu# stunnel -v
[ ] Clients allowed=500
[.] stunnel 5.56 on x86_64-pc-linux-gnu platform
[.] Compiled with OpenSSL 1.1.1c 28 May 2019
[.] Running with OpenSSL 1.1.1f 31 Mar 2020
[.] 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)
[ ] Deallocating section defaults