Are you located in an area where the rest of the region changed time zones but your area doesn't?
If you are in Arizona for example: The other states in your time zone will change to Mountain Daylight Time but Arizona won't because it doesn't follow DST.
You'll need to set your time zone manually to Arizona rather than Mountain Standard or Mountain Daylight Time (there's a separate time zone for Arizona). https://digibites.zendesk.com/hc/en-us/articles/200300033-Time-zone-issues
This is because your event times are tied to this; when the other states in the time zone switch to Daylight Savings Time, your old events will switch along with it. The same will happen again when they switch back to Standard time in half a year and you'll have the same problem again.
If you change the setting now it's still not going to fix the old events, this is because they were created using the old time zone settings and not the Arizona time zone setting, but it will prevent you from running into this issue again in the future.