Hoping this might help someone. I was having the same problem on Desktop for Mac. First I did the standard fixes, verified data, rebuilt data, tried restarting, etc. etc. Still didn't work.

By chance, the client had an apostrophe in his name. In the client list, I removed the apostrophe and it was then found by the system. I entered what I needed to enter. Then I went back, reopened the customer list, and restored the apostrophe in the client's name. It's working fine now. I think it had something to do with the apostrophe. This may not solve everyone's issue. But it solved mine.