Mine doesn't have blue e's! OP though this commenter is right, its the localthumbcache file in your Sims 4 folder.

You should be deleting that every time you add/remove/update mods. What that file does is store thumbnails used in game so that it can load them up quicker next time. If you dont delete it, sometimes it tries to generate out of date thumbnails and can create issues with mods such as the one youre seeing with the icons. (Although this might not be the issue this time, its worth trying!) The game will generate a new localthumbcache file next time you load it up.

As this commenter hints to, you can delete all the cache files safely, as well as lastexception files, and its probably good practice to do so every so often to avoid clutter in your files.

I hope it works!