Struggles with syncing podio calendar to google calendar

I experience problems with syncing my podio calendar to my google calendar. Most of the items are presented in my google calendar. However, the items with the agenda sign in front of it  (so in the picture below, on the 12th of May the activity "16:00 LV" and on the 19th of May the activity "externe training") do not sync and are thus not presented in my google calendar. All the other items do sync so it seems it has something to do with the characteristics of this kind of appointment. Do you know how to resolve this? Thank you in advance!