I thought I was going crazy this afternoon.
Updated a client’s site to 5.7.9
All of a sudden, a date field stopped displaying the correct value.
Did some SQL queries to verify (also tried a gazillion other things.. slight hyperbole) and the postmeta values were correct.
For a given postmeta value, looking at the field in the editor, I would end up with the right one sometimes, but most of the time, it would be a totally different value.
Example: 20190207 in postmeta would display as February 9th, 2019.
Played around with the display setting… all variations would display, baiscally, 20190209.
( as an example, many of the posts had the same problem ).
I was never able to track down the problem.
However, reverting back to 5.7.5, all seems back to normal.
Unfortunately, I didn’t try more granular reverts / updates through various versions.
Sorry for not doing more testing to be able to diagnose more specifically what was going on.