SharePoint iOS App Not Showing Calendar

Good morning...  New here, so I hope this is the right place to post.  I have a SharePoint 365 environment that is very, very simple.  Besides the default Communications Site (which we don't use), we have a simple site with only a few document libraries plus a calendar.  The calendar is not a "group" calendar, it is just a simple calendar that anyone (we have a very small office of 3 people) can add items to.  Works fine when using a browser.  We have the home page for the site configured to show documents plus events (using the Events webpart).  When we use the SharePoint iOS app to login and go to the site, we see calendar entries via the Events webpart on the home page, but if we go to the Calendar itself, nothing shows up...  The only thing that is out of the ordinary (if it even is out of the ordinary) is that our calendar has a LOT of items - over 5,700 - since we imported several years of calendar items from an older SharePoint on premise environment to our SharePoint 365 environment.  Could the number of entries in that list be causing the iOS app to have problems?  Or could it be something else?  We have not customized the Calendar list in any way (i.e., no custom fields, no changes to the default view, etc.)

Thanks for any thoughts...

Dave F.