iPhone XS Max keeps restarting and is slow after repair.

Hey, yesterday I finished restoring an iPhone XS Max that had a cracked screen and back. I replaced the screen with an original refurbished apple panel (works well), however used an aftermarket housing with small parts.

In the end I noticed a lot of the small parts were badly installed, or were missing. I needed to transfer over the speaker mesh and grommets, button springs, Taptic Engine (due to paring), screws (LOTS were missing), button and wireless charging flex (as the included one was not soldered), flash flex, wifi antenna flex and the usual logic board, battery and FaceID components, and that’s just what I can recall. As far as I could tell all the functions seamed to work fine, however…

The iPhone is incredibly slow, and very laggy - even using the keyboard there is a massive delay and sometimes freezes. It Alonso constantly restarts every couple of minutes it is used (even sometimes while it is charging - using a genuine apple cable and 20W fast charging brick). Initially I thought it was a battery thing, but the battery was working fine before and displays 90% Battery Health, then I found out that it may be related to the charging port, as one of the included parts I did use was the aftermarket charging port (the other one was quite dirty). I haven’t sealed the screen down with adhesive just yet, as I wait for a solution, but I don’t want to throw more money at it with its imminent depreciation coming with the iPhone 12S/13 around the corner.

Any ideas? Could it be charging port or battery related, or is it a logic board thing? Just a bit of a shame as the repair took hours and hours (probably should have spent the extra to get the housing and parts from my usual supplier!).

Thanks in advance (: