Unknown Javascript Engine Error (internal) and exceeded maximum execution time error

[ainthateasy]

Hi all, 

First up let me know if I'm posting in the wrong place and I can take this elsewhere. 

I am a developer with a Google Sheets add-on live on the Google Workspace Marketplace with a large number of regular users. I recently begun noticing these two errors coming through my Cloud Logging and Error Reports:

1. We're sorry, the JavaScript engine reported an unexpected error. Error code INTERNAL. 0[unknown file]([unknown function]) 

2. Exceeded maximum execution time  0[unknown file]([unknown function])

I am trying to debug and figure out what change I made that is causing them but both errors don't seem to come with much information, such as a specific line in my code. All I seem to be able to see is that they are occuring within my custom functions. 

It seems most likely they are a timeout error, but I don't know what could be spinning it's wheels in the code without any further info from the stacktrace... I use URLfetch, PropertiesService and Cache in my custom functions, could these services throw these sorts of errors? 

If anyone has any further info on how or why these errors are thrown that could help me identify the root cause I would be forever grateful.

Best,

David