There is a problem in EM Client V8 8.0.2820 where if you have current Gmail (recurring popup reminders) at eg: 8AM for every 2 weeks, but then want to modify one of these specific future popup reminders (to a slightly different name / title) and you haven’t dismissed the current reminder yet, if you change the name / title of one of these reminders in the calendar on the next recurring date, the “specific current popup reminder disappears from the current reminders window from today” even though i haven’t dismissed it.
So modifying any future specific calendar reminder name / title automatically dismisses that current specific reminder. I have replicated this issue many times.
The only way around this atm is to dismiss the current reminder and then change the name / title.