Its a bug since 1.78, try following: (for example)
- you have a meetup at 5:00 am but decline it
- you are free riding from 4:50 till 6:00
- The 5:00 am meetup join button will be gone as i declined it and its too late
- You have a 6:00 am meetup accepted
- At 5:55 the meetup join button is visible
- At 5:59 you click join meetup
- You are joining the 5:00 am meetup although its an hour late join → wrong
If you need any more information just shout out. Thanks. 