here’s a fun bug that took me all of today to solve 
…
The team uses a system where we have all these services that get required/initialized on runtime by one main handler and allows services to require each other without issues.
For some reason ONE of the services I am working with is being required twice, as when I tested by putting a print at the top of the module, it printed twice… Though non of the other modules did that.
I thought maybe the handler isn’t properly caching the module when it’s first required, but that wasn’t it… otherwise, all the others would have run into this issue…
I tried commenting out the parts of other services that use this module but that didn’t work either…
I tried replacing the print with error() to see if i can find out anything, though because of how error works the handler just stops running and so I didn’t get my two errors i was hoping for…
I had no clue how this bug is happening, or how I can find the cause…
At the end of the day, one of my team mates came on and saw I was having this issue and suggested to use debug.traceback(), I had no clue that existed or how it worked. After looking it up and then using it, I immediately found my problem!
I was using the handler to require the module, however, the paths i gave the handler in each of the two other service i was requiring from were not the same…
one used game.StarterPlayer.[path] and the other users player.PlayerScripts.[path]
I did not catch that at all as I was working to find the issue, since my thoughts were set on that its an issue with me calling some function incorrectly.
take aways
- Always be consistent with how your code operates.
- debug.traceback() is a godsend!