All day events created in Google Calendar with a reminder set at a specific time on the same day (e.g. 09:00) are not shown by Thunderbird Calendar (Lightning)
If I create an All-day event on an Android device there is a reminder can be set on the day of the event at any time during the day. These reminders are shown on Android devices synced to the calendar, and on the Google Calendar web page.
Thunderbird's calendar shows the events, but no reminder. Any reminders set at the start of the day or before do show up on Thunderbird.