Just tried the new relase and got this weird behavior: I can't use a direct connection to localhost:27017 (it still works fine with 1.3.x).

Same here, but 127.0.0.1:27017 works. Arch Linux, mongodb 4.4.0
Haha didn't think about trying 127.0.0.1, working too.
Hi @jflebeau , @vdemin , thanks a lot for reporting the problem. We just released today officially, hopefully with the fix for this issue. Could you please make a quick check? https://robomongo.org/download
Yup, working.