Calendar entries are migrated in the wrong time zone
Ensure your users have the correct time zone set for their calendars (source matching destination).
If migrating to Exchange / 365
You should configure the correct time zone in Destination Platform Settings / ‘Exchange/Office 365 Calendar Timezone’, to avoid any possible mismatch.
If migrating to G Suite
You should configure Destination Platform Settings / 'Default Calendar Timezone', which will apply the configured time zone in case a time zone is not found when migrating appointments from the source.