End date picker broken

Using: Ultimate Auction Pro 7.4.8
PHP 7.2.10
WP 5.3

When adding a new auction, start date picker works fine, but end date does not (no calendar pop-up on click). It might be a compatibility issue with recent WP 5.3 update, which changed backend button styling. I disabled all plugins, to test if there’s a conflict with any of them, but the problem persisted.

I can work around the problem by inspecting the field in browser and deleting readonly=”” from html code, which allows me to type it in.