Any bank could close an account in the UK if there is no activity for a long period of time. I had HSBC accounts, Hong Kong, Singapore and then UK. Never had any problems.
So if you enter on 60 day exempt and have a return ticket for 90 days, the immigration are aware you can get a 30 day extension from immigration while in Thailand, so therefore should not stop you entering.
I used to do every thirty days, sometimes for a few months when work was scarce. Never got questioned and I used to border bounces everytime. It wasn't until ten years after I moved to Thailand that I got Red stamped. So did ok. Still let me in for thirty days, so went back to my country and got a non O multiple entry.