Oh boy, I have a lead! And it's NOT related to #TLS. I finally noticed another pattern: #swad only #crashed when running as a #daemon. The daemonizing wasn't the problem, but the default logging configuration attached to it: "fake async", by letting a #threadpool job do the logging.
Forcing THAT even when running in foreground, I can finally reproduce a crash. And I wouldn't be surprised if that was actually the reason for crashing "pretty quickly" with #LibreSSL (and only rarely with #OpenSSL), I mean, something going rogue in your address space can have the weirdest effects.