Sounds like the screen was damaged by the impact. Repair or replacement required. Maybe costly $$$.

 

I think the answer to that is that the people that produce and sell these things know that a 'new' model is going to come out 6 months to a year after you buy one.

What better way to ensure that you will 'want' a new one that soon than by making the one you have out of glass and cheap plastic?

 

Looks like it.

Is that the cheapest one on the page?
Why does it say something about 'open box' in the description?

Is it worth the risk/effort to save $5 over one that hasn't been opened?

How much was the phone to begin with?

 

I am not familiar with your skill set as far as R&R of phone parts.
You have surpassed me, because of what you have done already.

I fix larger things, hahaha.

Anyway, you now face a conundrum, as far as the part is cheap- but can it be trusted, and can it be successfully installed.

How much is a new device of the same calibur?

And what exactly are you doing that needs so much memory?

I only ask that because I am a fairly constant, heavy user and I make due with a 2GB device with 16GB internal & 32GB SD card, which was $40 brand new.

When my battery went south, it was cheaper and easier to get an identical device.
So, now I have two, one that I use for media at home, and another for games, this, etc.

My actual cellphone is another device entirely, and it is only 1GB & 8GB internal with 32GB SD card.
Believe it ir not, because it has the Android Go (8.1.0) OS it almost keeps up with the 2GB devices.

 

Given you only spent $40, I don't think it's worth investing too much money on repairing it. Your data on it is probably worth more than the phone itself. Even with the display drifting around if you can back up everything you need to save, it might be best to just migrate to a new or newer phone.

But if you do want to try and resurrect this phone, since you did try and re-seat the connector and confirmed that the problem is still there, keep in mind while the problem could just be the screen, this does sound more like the underlying digitizer is the issue:
Screen
https://www.ifixit.com/Guide/LG+G4+Screen+Assembly+Replacement/125127
LCD and Digitizer (well over what you paid for the phone)
https://www.ifixit.com/Guide/LG+G4+LCD+and+Digitizer+Replacement/88932
and if it is something else like just a solder joint on the logic board being weakened or broken (a likely occurrence from an accidental drop) that would involve a more extensive, and pricey, repair.