Welcome to RStudio Community!!
Whoa! Yeah, a lot can break on OS changes / etc.! Also, that is a big upgrade jump!! (Worth noting that RStudio is now on version 1.4, so 1.2.5 is still like 1.5 years old).
In any case, I would look at the output of systemctl status rstudio-server, cat /var/log/syslog or cat /var/log/messages and netstat -lntp to see whether RStudio Server is alive, listening, and what it's doing 
I hope that helps!!