My digitizer seems to be malfunctioning. Need help with diagnosis.

I recently replaced the housing of my 6s for a new one. Everything works, but not properly, like the screen and top speaker.

After using the touchscreen for a while, the touch “stays” in one spot on the screen. I checked it with multi-touch test app. There’s one spot of 1cm radius, where the touch stays constantly on, or is registering rapidly. Putting device to sleep and waking it up solves the problem for another minute or two. Could it be caused by a damaged flex connector from the digitizer? Is it more probable that I could’ve damaged the socket on the motherboard, or the connector on the cable itself? I’m concerned, as the socket might be damaged and I don’t want to buy a new screen just so it can have the same issue.

Another thing is the speaker. Sometimes during the call it gets really silent and barely audible, but it may (or may not) switch back to normal operation. Which cable is it passed to the motherboard from the display assembly? (digitizer?)