Google Calendar: events dont end up in calendar after accepting the invite

I am experiencing the following challenge when accepting Google Calendar invites:

→ When clicking the green eM Client button “accept” (to accept a cal invite), the event will actually NOT be accepted into the calendar. It does work with MS Exchange or Apple iCloud events, but not with Google events.

→ Instead I need to scroll down the email notification until I reach the google window. I need to accept the event there (in this google specific panel) for the event to end up in my calendar

The confusing thing here is that after doing the first “accept” (on the eM Client button) the text will turn to “you have accepted the event” kind of text. But the event never ends up in the calendar.

is this a bug or could this be fixed via some settings?

Many thanks