A series of issues.

This is starting to get really annoying.

Unfortunately, server resources are not unlimited, so a limit of 20 site pages per minute from one IP has been introduced.
This helped reduce the load and more or less stabilize the situation.
Without the restriction, the forum becomes easy prey for DDoS attacks and bots, and in all likelihood, then all users would receive no response from the server at all, or would get a different error message instead.

Nevertheless, after your message, I increased the limit threefold — now it's 60 pages per minute (which is quite a lot for a human user). If that isn't enough, let me know, I can set it even higher, but the higher the limit, the more vulnerable the forum becomes overall.

Lately, besides open bots that don't hide their purpose and identify themselves as bots, a large number of "guests" have appeared who identify themselves as regular users — yesterday there were about 4500-5000 guests.

Today there are twice fewer, but still. At the same time, based on address geolocation, most of the guests are from Brazil and Vietnam, which makes it highly questionable whether these are people rather than bots disguised as humans.