unchecking auto configure and entering address, port and transport only
Jitsi does not register.
If I also uncheck the parallel DNS resolution in the advanced options tab,
Jitsi register without problem.
Usually the parallel DNS causes problems if your network blocks queries to "foreign" DNS servers. By foreign I mean servers outside your network, e.g. Google's public resolver. We try to use this external resolver if we don't receive a reply from the main DNS server within 1.5 seconds.
Could you describe your network setup and post the logs () so we can better understand your problem?
Why this problem was inexistent 3 or 4 month ago?
There were some changes in the code that does the SIP REGISTER. We no longer do a DNS lookup of the registrar address as it might only be known to the proxy and do some additional DNS lookups for the proxy auto-detection (specifically to _sips._tcp.yousipdomain and _sip._tcp.yoursipdomain).