I had a similar issue with my Galaxy S4 a few years back, when I first started getting interested in repairs. I had accidentally snapped the head off the antenna so it obviously wasn’t connected. I only realized it when my signal was crap and I had to buy a new antenna. It may also be due to the charging port connector as Ian Shalongo said.
Before you go ripping your phone apart though, you should try a few things…
Try rebooting the phone.
Check for any updates. Many Pixel 2 owners had signal problems that needed an update to be fixed.
Try basic trouble shooting steps like popping the SIM out and back in, resetting network settings, etc. There is a really good guide for
Good luck and God Bless