Most posts seem to indicate that there generally isn’t any issues entering. There have been a couple of posts where people have been questioned but eventually let through.
I guess it’s like many entry issues. If the IO is having a bad hair day you may have issues.
You can’t convert from a OA to an O in Thailand. You would have to let the OA lapse and leave to re-enter visa exempt or buy a tourist visa to convert to O or buy a O prior to arrival.