Shared Hotmail calendar not syncing on iphone

My husband and I both use hotmail calendars on our phones and can view and add events to each other's calendars. Very recently, his calendar stopped updating (won't add new events) on my phone. I can still view his calendar, and events that were entered a long time ago (like recurring ones) still show up. My calendar seems to be updating fine on his phone. We've checked our settings and they seem to be the same. We both have the iphone 5s and recently updated to ios 11.2.6. Note we are not using iCloud calendars and never have, so I don't think that's the issue. We share the same Apple ID (which is his hotmail account), but I don't know if that's relevant.

I did see some other suggestions to delete the account and add it back, but those options don't seem to be available in settings or in ical itself. Any help would be greatly appreciated!