We've been banking with Kasikorn (green bank) for 6 years now. No problems.
We have friends with Krungsri (yellow bank), and they like it. I don't remember if we had to get compulsory insurance or not, we were just excited to have found a bank that didn't give us the runaround, like Bangkok bank did. It was awful.
** Always remember, with any of these banks, you must ASK for internet banking!
Be sure the insurance will cover if you're asymptomatic or negative, because if you test positive and have no symptoms, OR if you were sitting next to someone testing positive, you must go to hospital for 10 (14?) days.
I have a friend who is Un V'd. He's been traveling to Bangkok and back quite a bit. Sometimes they ask to see his cert. He says "no", and just looks at them.
Try using Google Chrome. Also, the phone app doesn't work and never has.
Don't allow the site to autofill your saved information. Type all of it in yourself. When it auto fills, it won't work.
The only autofill you will need to do is choosing your home country, Thai district and city. Hopefully, that will work for you. We've done it multiple times.
We've been in TH for 4 years on Non O. Just got a new extension of stay stamp a week ago. Now we have to do 90 day. We have been using the online method with success. But now, it's not working. How long does it take for the extension to get into the system?