Hey Chris,
Thanks for this information and your patience here.
Quick question/idea:
• If you head to Events → Settings in your site’s wp-admin, scroll down to the option called “Timezone Settings”.
• What is the option currently set to?
• Try setting it to “Use the local timezones for each event”, as shown in this screenshot:

☝️ Do this then take a look at affected events — does anything improve?
Cheers,
George