I have forgotten the exact reason but it had something to do with not having a valid payment method. Some change on Google Cloud end triggered it - they were billing initially with the Singapore subsidiary and when they changed it to the India one, something had to be done from our end. Hardly got any notices and also we had around 100k USD in credits at the time. Got it resolved by reaching out to some high level executive contact we got via our investor. Their normal support is pretty useless.

I've read about this happening a lot with google cloud

If your payments fail for whatever reason google will happily kill your entire account after a few weeks with nothing other than a few email warnings (which obviously routinely get ignored)