FIXED - $8 Flex cable replacement from Amazon (pictures and links below).
Context - 5 months of unpredictable loss of signal (unable to use data, make calls ect - unrelated to signal strength) on a Samsung Galaxy s21 Ultra on Google Fi. Trouble shooting through Google FI completely useless. Changing carriers did not fix the issue.
CAUSE/FIX - a broken connector for a the flex cable that apparently connects the main motherboard to the USB C port. I replaced the part at home with a Y0 size screwdriver and a hair dryer (to warm the back plate). Only took ~15 minutes following a basic teardown video.
This was the replacement part from Amazon:
This was the most helpful YouTube video:
https://www.youtube.com/watch?v=cU3QXPoFOUI
For reference he touches the broken end of the flex cable at exactly 5:14 in the video
Here is a picture of the broken cable from my phone. If you look closely at the port at the top (SUB side) you can see the connector is broken.
Here is a photo from inside the phone.
Note that the circled side has a broken piece of the male connector that I had to remove with a small set of tweezers. The arrow points to a broken portion of the female connector. I was worried I would need to replace the entire USB C board but the connection has been flawless so far despite the fact the board (female) side looks broken. I will update this post if the connection issues come back.
Hope this helps someone - ewaste is such an issue I'd hate to see a phone thrown away for such an easy fix.
