You tried to talk to the US SS office or the one in Manila? I’ve been able to communicate with the Manila office by email. They have responded within a couple of days. Tell them you are living in Thailand.
The proof of life letter is not that harsh. I moved from Bangkok to Sisaket province. Last year when I got the letter it said that it was my second notice. I sent it back by EMS and there was no interruption of my benefits.
I’ve heard several times that if you constantly check the interview appointment calendar that you can sometimes catch an earlier appointment when someone cancels.
The OA requires insurance. The O doesn’t require insurance. Aside from the insurance requirement they both have the same exact 1 year extension requirements. Go for the O visa.
I had an OA for 6 years. As for the better visa . . . I switched from my OA to a 10 year pensioner LTR visa.