I saw on the internet some filament guides for spool holders for Prusa Bear printers or similar ones with 2020/2040 profiles and after trying, I was able to verify that the filament came out of the guide in extreme movements of the X axis. So I made the opening diagonally on the front, it is impossible to pull the filament out of the guide with this mod.

I have also strengthened the design so that when manipulating the filament guide you cannot break it.

Try it!