iCal syncs with iPhone with wrong date and time

I have an iPhone 7 and an iMac running Mojave 10.14.5. I use iCloud to sync my calendar between the two devices. Until a few weeks ago new entries on either device synced perfectly. Now when I add a new event on one device it shows up on the other device as much as 3 days off and at a very different time. I have checked the time zones and other date/time settings on both devices to make sure they match (they do). Any suggestions for how to fix this? I rely on the synced calendars and really need them to match, and would prefer not switching to google calendar.