Hi there,
I seemed to have the same problem with a FP3+. Even swiping upwards to get to the the keypad to unlock the phone was impossible.
I think I resolved the problem with opening up the phone and cleaning the contacts of the screen with isopropanol. Additionally I also took a flathead screwdriver to carefully scratch a bit on the metal areas of the screen which get in contact with the mainboard shield and cleaned them with isopropanol (handmarked red in the picture). Then I took the flathead screwdriver to bend the contact pins on the mainboard shield a few mm upwards (handmarked blue in the picture).
That way a good electrical contact between the mainboard shield and the screen is ensured. After reassembling the issue didn’t occur anymore (at least so far but I am optimistic).
Maybe this helps somebody.