Hi,
I may have found similar case with you. In my case, this happened on one of the users that use Chrome browser.
What we do is deleting the service worker, and refresh the PWA so the browser can get the latest service worker.
In Chrome, this is done by opening "Developer Tools", then open "Application" tab. On the "Service Workers" choose "unregister" (idk if "update" can also fix this, but in my case, we tried "unregister" and everything works again).
It seems the service worker is failed to update to the latest version.
Thanks