Here is a sample module that does the required task.
https://github.com/stpaultim/field_change_log
I'm still working on it and testing it. But, initial tests are good. ...
Probably not the reason, but worth to do a quick check:
Sometimes the update cache interferes, so if something's odd with updates - some module (or core) claims to have updated, but then...
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Just seeing if anyone has any ideas on this one?