Hello -
The Cloud Build system has logged a burst of internal errors, resulting in some build failures due to internal errors as well as slowness in the API. It’s being investigated and worked on now - more to come.
Update - the main issue was resolved earlier this morning (not long after that update above), and all polled builds are resuming now as well. Cloud Build is running some short queues in production now as it catches up with pent-up demand on polling, but those queues are clearing rapidly now as well.