Validation does not work since v5.3

Hello,

I started a topic in MB Relationship section, you can find it here for more details, but to summarize :

I'm using a complex form in a custom post type with several scripts to dynamically handle which fields appear and which are required, and all data is saved and retrieved from a custom table in database. Thus I can not use MB methods to recreate this form.

I'm only using Meta Box plugin for its MB relationship extension (which works like a charm to connect my CPT to posts and taxonomies).

For a few months, required fields stopped working in my CPT, I can save / update a post with empty form. Turns out the problem appeared with version 5.3 of Meta Box plugin (works as intended with 5.2.10).

Any idea of what may cause this in the MB plugin ? Is there a way to "patch" this manually ?

Thanks by advance