Thanks for the test! So do I understand you correct that with mainline/older version you have a freeze/crash but with latest it works properly? I.e. on jolla 1 mainline rockpool crashes on the call end, but on jolla c the whole phone freezes, while latest beta works ok on both?
To prove if that's not the case you may check before restarting the service it's status (systemctl --user status rockpoold) and see when it was started last time.