New Install, with external SSL terminator with Let's Encrypt; Mac OS X client refuses

System running OK otherwise, and could connect using Android client as well. But mac client resuses and says something about SSL handshaking.

Is this a known problem in Mac client?

Hmm. Seems that it actually works with Lets Encrypt Cert, but not with Cloudflare, which was on my route (I forgot that initially). Mac works now as well.