This sounds like a bad solder joint somewhere. Did you have to re-flow any solder joints to get the the test points to read correctly?
I’d re-flow all the solder joints on the board, especially the parts dealing with the signal path. Take your time and make sure there are no bridges anywhere. Also make sure you don’t use too much solder, which can be difficult to control and has a tendency to bridge other joints.
Good luck.
-Brach