Why is my iPad stuttering after battery replacement

1st gen iPad Pro 12.9 cellular 256GB

Replaced my battery with an iFixit replacement. After putting it all back together, everything *seemed* to work fine but the system was slow to boot and get into a usable state. Wifi was slow to connect at first and the system seems to be stuttering/freezing, very noticeable when multitasking such as split screen w/ YouTube and web browsing.

It’ s almost as though it’s thermal throttling or something, I noticed a thermal transfer pad on the PCB that should contact with the metal shield over the board. Do you think maybe I messed that up?

Running iOS 15.0.2.