Attendee's calendar schedule with no end date disappeared from attendee's calendar

[qb3450]

I have a users who are attendees of daily and weekly Zoom meetings and for some reason, one or two attendee's calendar schedule would disappear and they wouldn't get the reminder or the address of the ongoing scheduled meeting. Everyone else's calendar schedule is fine except for one or two and I've heard this for a couple different meetings. I'm just wondering if it's a Zoom thing or if it's Google Calendar that's causing the meeting schedule to disappear. Any insight would be appreciated.

Thanks