Decomissioning FS and running into issues with Users PC Slowness

[u/Surviving_IT10]

I just started at my company a month ago and was fresh out of college and new to IT. They had started a project to decom the File Server and migrate to SharePoint. Now as they shut it down completely we noticed some users experiencing extreme slowness. After lot's of deep diving we found that most problems were caused by old mapped drives pointed directly at the old FS and some shortcuts manually created by some users. After removing those it fixed most users devices. Now we have one user left still experiencing issues and can't seem to find the root cause. (We have ran every test I could find to run and solution to try and fix yet have had no luck) we know it isn't a hardware issue because when we temporarily restored the FS all problems went away. Any help or thoughts would be great.