We have had a response from 3cx via our partner.
------
We have received confirmation, and it appears to be an issue with the latest version of Chrome.
In the past week, Chrome released a number of updates, and one of them seems to have caused this issue.
It's worth noting that we observe similar behaviour with other PWA apps (not 3CX) in Chrome, such as Google Chats.
Additionally, we do not encounter the same issue with PWAs on Edge Chromium
------