The lumps on my betta weren't bubbles, they were solid and lumpy. They weren't white, though it's hard to tell with a dragonscale betta. The lumps never disappeared, the first would grow bigger then sort of deflate and within days it was back bigger than ever and always in the same place. The smaller lumps appeared after the first and they always stayed the same appearance, just more of them and getting bigger.
I did try treating with the strongest anti bacterial medication available in the UK (not an antibiotic) but it did nothing.
So what could it have been?