TOPIC:

Hi, in my Joomla! 3.8.13 and JEM 2.2.3 (and 2.3 dev1) I can't choose more than one category.
Earlier I could choose with Alt GR more than one category. Now (I don't know exactly since when) the first choosen is lost, when I choose the next one. This should be fixed, in a kind like in general joomla! (I will post this in github too).

EDIT:
I can't post it on github, I have strange problems to post an issue!

I think something is broken with your computer
On my test page it works on frontend as well as on backend. I use Control-Key (STRG or CTL) to select multiple categories for an event - no problems.

Oh no,
STRG or CTL works fine, but ALT+Gr doesn't work anymore! I don't know because of Joomla or because of JEM

e.g. I can choose the whole list of categories with STRG or CTL, but one category between the others I don't need, if I disable this category, this category is choosen and all the others not.

uups: now I've seen how, this is quite new for me! Sorry!