Not every border allows nationals of countries with a bilateral agreement with Thailand to border bounce. Mae Sai is one of those borders. This was not a ‘visa run’ as there is nowhere on the Myanmar side of that border where anyone can get a visa. So, a sign saying ‘no more visa runs’ is somewhat superfluous.

There are roads on the way to Mae Sai that do indeed lead to the friendship bridge in Chiang Kong that crosses into Laos.

Great report. One small thing though, if you crossed at the Mae Sai Tachileik border crossing that's not the Friendship Bridge :)

The 90 day report is for reporting the fact that you are in the country for 90 days. If you're not in the country for 90 days then you don't report that you are, because you're not. :)

I'm impressed that you managed to get that meaning from those words.

Probably didn't let them fly due to no ticket out of Thailand within 30 days of arrival, not the cancelled visa.

Sounds like a plan. If they say you do need insurance, then I would recommend you to go get a new visa (Non-Imm O type) and start your extension again from that.

Your visa is a thing of the past. You are here on an extension of stay. Your initial extension was based on a Non O-A visa which means that subsequent extensions for retirement would mean you meet the condition of requiring health insurance under the new rules. Now, whether or not a subsequent extension based on marriage still means that you will need insurance is something that the immigration office will know the answer to. Did you ask them when they did the pre-check you mentioned?

When my flights from the UK to Thailand have returns after 30 days they ALWAYS look for a visa in my passport. When asked what would happen if there wasn't one, and I didn't show a ticket out of Thailand within the 30 days as an alternative, they said I would not be able to check in.

I would get the visa. You may not be able to board your flight from London without one. Yes you can get a re-entry permit before you go to Vietnam.