...this one is most likely a DNS issue. Check the /etc/stunnel/stunnel.conf file and make sure all the Domains resolve when testing with PING at the command prompt. Also enable logging with the below code, and it will complain if there are name resolution issues.
output = /var/log/stunnel/stunnel.log
debug = 7
; foreground = yesAnother telling symptom is if the stunnel service takes a really long time to restart. Oh, below is the /etc/stunnel/stunnel.conf file segment that is for this very site (with some information obscured). For some reason DNS was having a glitch and caused the above error.
[parsoid.terrabase]
; wxyz = Port Number
; W.X.Y.Z = IP Address
accept = 0.0.0.0:wxyz
connect = wiki.terrabase.info:wxyz
; connect = W.X.Y.Z:wxyz
cert = /PathToCertificates/wiki.terrabase.info/fullchain.pem
key = /PathToCertificates/wiki.terrabase.info/privkey.pemAnd as usual, this is not a step by step fix it guide. This is just a hint or clue to get you going if you're using Google, and turning up a bunch of junk. Hopefully this hint helps someone.