Recently I have been seeing my Microsoft O365 add-in load with this error:
Error Image ADD-IN ERROR Sorry, we had to restart because this add-in wasn't responding.
The console/dev tools shows no error logged at all and then the add-in procedes to restart and run just fine. Is there any reason why add-ins fail to load on occasion without specific errors?
By default, web add-ins are restarted if any action takes more than 330 ms (5s). You can use a WebWorker to launch long-running tasks. For example, see Long operations crash Office addin (JS).