IA> Okay, I solved this. Documenting for anyone else who has this issue:
 IA> 
 IA> cryptlib 3.4.6 didn't work for me, but did generate a faulty ssl.cert
 IA> file in "data". Trying any other version would thereafter fail (earlier
 IA> versions wouldn't even load and listen, but 3.4.5 would fail because of
 IA> the bat cert). Shutting down mis, 
 IA> removing the cert file, replacing cryptlib with 3.4.5, starting it back
 IA> up, trying a connection to let it generate a new cert file, and then
 IA> reconnecting did the trick.

Thanks for the update and for letting us know!

3.4.5 is the version the website says is supported.

As you've found there is a 3.4.6 beta but it does not appear to work, unfortunately.  I did spend some time to try to figure out why but I wasn't able to.  I was mostly waiting for a 3.4.6 final version but it seems this beta/release candidate has been around for a long time now so I may need to rethink that approach.

... System halted - Press all keys at once to continue

--- Mystic BBS v1.12 A48 2022/04/26 (Windows/64)