After replacing the screen twice, my iPhone 5C clicks in weird places.

So I run a small town repair business at my high school. It's only existed a few months, and on my 3rd device, an iPhone 5C, things are going waaay wrong. And I'm struggling a bit. Care to help?

I am not hasty or impulsive at all when it comes to repairs. I have an ifixit toolkit, a magnetic project mat, ischlack, and everything one would need to do a repair effectively. When I do repairs, I have iCracked's full length replacement video as well as iFixit's guide open (mostly for screw sizes). It takes me about 2 hours to do a repair. So when I gave the device back after only some basic testing, and the poor girl reported the phone having an unstable touchscreen, I was really nervous. I took it home and tested it, and sure enough, the thing was a mess. It kept scrolling all over the place, the screen straight up stopped working at minute intervals, and browsing through apps like the notes section or instagram were impossible - jerking, rapid movement, the whole shebang. I took it apart again and examined the pins, and nothing seemed out of the ordinary under my magnifying glass.

iFixit, my parts supplier, graciously sent me a replacement after 1 call.

Now, I've just finished the second screen replacement, and things are better, but unacceptable still. In spurts, the screen works beautifully, like new. But within a few seconds, it has now decided to click random apps, go completely nuts and pull down search every 2 seconds.

This is a paying customer. My buisness will shut down if I have to borrow a few hundred dollars for a new phone. I simply wouldn't be able to pay it.

Will a hard reset help in this situation? Could it be the software is rejecting the new hardware?

Please, please help.

EDIT: Also, I should mention that oddly, the screen resets this spasm right after you lock it and unlock it again.

I also just tested it with a timer - spasms can take 5 seconds to a minute and a half to occur.