Intermittent soft key malfunction after opening case to replace camera

I just replaced my S7's camera module and lens, which involved heating the edges, prying off the rear cover, removing the three modules and motherboard, and replacing the camera itself.

After re-assembly the new camera works, but every once in awhile the phone behaves as if there are a flurry of touches on the menu soft key; the apps menu pops up repeatedly as if the menu were touched, sometimes the two most recent apps alternate as if the menu were swiped sideways, etc, all without touching the screen at all. After maybe 10 seconds of this (or, it seems, possibly right away if I use the power key to lock the screen immediately), it calms down and everything seems to work perfectly fine for awhile, until it happens again.

Any ideas what might cause this kind of malfunction? Could it be as simple as a loose connector when I re-installed the motherboard? Or, I read that the screen is sensitive to heat, does this sound like a symptom of heat damage to the touch screen from when I heated the edges to open the case?

Is there anything I can do to further diagnose and fix this issue?

Thanks!