I’m a U.K. citizen but got my COE issued online from the Washington Embassy as I was in the USA. That was in April. However I couldn’t get a visa that wasn’t issued by my own country of residency. In my case I used the visa exemption to enter and then changed at immigration inside Thailand
The COE isn’t anything related to you visa or visa exemption. It’s just checking your insurance and inbound and outbound flights along with your ASQ booking.
I’m a UK citizen but mine was issued by the Washington Embassy because I was in the USA. However I was advised that I should be making the application for a visa to the embassy in which I’m resident. As that wasn’t an option the guidance was to enter on the visa exemption which gives 45 days, but can be extended while in Thailand to give an extra 30 days.
I took a route from US to BKK, via NRT with Japan Airlines last week using visa exemption. No issues at the US check in. They recheck all documents and visas in Tokyo after the bag security check and you’ll need to tell them again that you don’t need a visa (or at least I did).