Items from some categories don't show

Since very recently my calendar only shows the events created in two categories, while I have events in 9 different categories.

None of the categories are private.
All of the missing/hidden events exist in the database.
Selecting one of the “hidden” categories on the calendar page results in an empty calendar. Selecting “All categories” brings back the two visible category events, but none of the events from the other categories.

I have checked the settings…
I have generated a new shortcode with a specific mention of all the individual categories and I have tried every other thing I could think of, but none of it worked.
The categories remain hidden.

What could it be?
Help… please…?

https://wordpress.org/plugins/my-calendar/