I don’t see anything in the recent changes that specifically addresses this:
= 5.3.9.2 =
* Time Picker field: Added compatibility with previous 3rd party field settings
* Core: Fixed JS error setting l10n for Select2 with 3rd party libraries
= 5.3.9.1 =
* Time Picker field: Fixed bug causing value to appear as current time
* API: Fixed bug causing have_rows() to fail when using an object as $post_id parameter
Unless it had something to do with the last one, maybe.
