Im wondering if it might be a specific software you downloaded? I haven't had that type of issue with my iPad Pro, but for instance MLB app on my Apple Watch singlehandedly kills the battery quickly and doesn't allow the watch to charge to full. Deleted that app....problem gone.
I got an iPad Pro 10.5, 256Gb, Space Gray a couple of weeks back and it too had an issue with restarting..
It had I0S 11.2.5 OOB and had not even had 3rd party apps installed. I did a DFU re-install to 11.3.1 and it started the restarting glitch again later in the day. Apple did a remote diagnostic test whilst it was still alive and stated that the blue tooth module was broken and that's what could be prompting restarts... back to the store I went.
Bizarrely I then got a curved iPad - straight out of the box. On the advice of Apple I swapped it and I now have a flat, fully functioning iPad with amazing battery life