tl;dr
We have a number of background processes that execute periodically on our systems; one of these is the one that resets the amount of CPU used, so that you get a fresh allowance every day. Early in the morning of 2024-05-03, on our US-hosted system, that service failed silently.
Unfortunately, we only realized it was not working on the morning of 2024-05-04. Putting a fix in place required another day.
At the same time, our load balancing system was experiencing a DDoS attack by malicious bots, which led to an overall decline of performance.
For some of our users, who noticed the CPU issue, these two separate events correlated, leading to confusion.
These issues appeared only on our US-based system – users on our EU system were not affected.