Hi aprilp2020,
Sorry for the inconvenience it may have caused.
In case the issue related to a specific browser, I would like to suggest you open the list with other browsers or in-private windows then check the result.
And to further check it, we need you to provide some information:
- Whether all lists affected in this subsite? Or just some certain ones?
- When did the issue start occurring?
- If all members in the subsite encountered the issue?
- If you have created a custom view in your SharePoint list? Or when you try accessing the default calendar view you received that error message?
Thanks for your time and patience.
Best regards,
Madoc