Same issue here. Some reminders work, others don't. I notice it, as previously mentioned, where individual occurrences are having their reminder set to "None" while the meeting series is set to a value. Also as mentioned, the occurrence is NOT broken from the series (no slash). Works fine on Android mobile app, but not PC desktop app. Causing major issues at work for me.
I am noticing the same manifestation. The meeting series is set a have reminder, but an individual occurrence has the reminder set to "none." The individual was never edited to be different from the series. So there is no reminder for the meeting.