I had the same problem for 4 days this week on feddit.online (PieFed instance). My CPUs were pegged suddenly, and the database load that is normally like 1.5 spiked to 15. The UI became unresponsive, and gateway timeouts became common. After 4 days, yesterday morning, it just suddenly stopped. I didn't have the opportunity to investigate.
I'm hearing about scraper attacks from other instances too.
I'm going to try to do some forensic analysis this weekend. If you find a way to identify these scrapers, please share. If I learn anything I'll share too.
Good luck!