This may add some noise to the thread, but I want to remind people to #contactsupport if they experience the issue after disassembling and reassembling.
I had issues with ghost touch in my FP3, as this thread shows. It was a combination issue of a faulty digitizer, which I got replaced, an a loose connector on the received display. The issue took some time to resolve but thankfully I was able to replace the display myself and didn’t have to spend significant time without my phone. In your ticket to support I suggest you link this forum thread and also send some similar diagnostics as to those that are included here, it can reduce the time it takes to get a response.
Also anecdotally I wanted to share the times when I observed the touches on my FP3 getting worse, before I got a replacement display and firmly seated the connectors - they seem to match with the issue you see on the FP4.
- multiple apps and tabs open
- high temperature above 34C
- sometimes, plugged into certain chargers