In recent years, spam (unwanted messages) has migrated from email to SMS to calendar events.
Image Credit: jewels256
While most calendar providers will remove or block these events automatically, some will only suppress the events/calendar, rather than removing them.
This creates a problem when that calendar is shared with other services, like TRMNL, via an .ics file, the standard for sharing calendar information. If the events are still present in the .ics file, they will show in your TRMNL calendar.
The clearest sign of this problem is if events appear that you do not recognize, especially if they are in a language foreign to you.
To resolve this issue, you need to purge these events from your calendar at the source (Apple Calendar, Microsoft, Google, etc.). Once that is complete, you will be able to Force Refresh your calendar plugin to get the new, clean .ics file update immediately.