Hasn't happened to me. What has happened is, when we were doing correspondent lending and we were originating some loans, we would get to the finish line. The end buyer would turn around and pull the plug at the last second and would make us look bad because they either would not buy the loan or wanted the terms changed.
Yup I see this too from time to time. Especially on the niche financing that requires multiple exceptions, appraisal revisions/transfers, unique properties or a bunch of LOEs.
From the lending side, I will add this: always get the full term sheet in writing before you pay for appraisal or lock in closing. Rate means nothing without points, fees, prepay, and draw schedule. If terms change late, ask what changed - appraisal, credit, property condition - and get the new terms in writing. If a lender cannot explain it clearly, walk away.
Yes, it has happened to borrowers I work with. The ones who had everything in writing were able to push back or switch lenders in time.