I think you were just unlucky on the day and got an immigration officer in a bad mood. You will always get more hassle when your passport is full of stamps. Just the way it is. It seems you are not breaking rules, or even abusing the system like some people who have back to back extensions are. I would just forget about it and carry on as you are. To make life easier, I would probably book a very cheap flight out of Thailand within the 30 days to prove your intentions. Yes, this might be wasted but this is actually a requirement anyway.
P.s. your written English is great, so I very much doubt spoken English was a factor here, especially when most IOs don’t speak much English themselves.
Arrived on 1st January. First checkpoint at the airport they want to see negative PCR, Thailand Pass and passport.
Immigration then wanted to see my e-visa printout.
After baggage claim came the PCR test. Initially on approach they want to see you’ve got the psas booking confirmation and then at the actual desk they asked for the psas confirmation and hotel confirmation.
I had print outs of everything though just to be safe. There’s actually a place now you can print the documents at the airport. You go to a diffident queue and once printed rejoin the back of the main queue.
I’d apply for a tourist visa before you go and you get 60 days as mentioned above. That way you don’t have to mess around at the local immigration office while you’re here. Visa application is all online nowadays and don’t even need to send your passport to the embassy anymore.
You could get insurance with Safety Wing.. it’s pay monthly @ 42 USD per month and you get a confirmation letter 15 mins after buying. Cancel any time. The confirmation says it’s valid for 1 year from the date you purchase. I’ve just used it myself for the Thailand Pass.