any help finding out what is the cause would be great!
General advice here.
What is the domain?
Looking at your DNS records, all your records are gray clouded:
Essentially what this means is that Cloudflare will not proxy the DNS records but only resolve them. The reason you’re still seeing Cloudflare branding on your error codes is because the records are pointing to another Cloudflare customer.
So there can be 1 of 2 issues here. If you don’t have an origin server (host) and they are your host then, you should contact them directly and request assistance on the issue. If they’re just a middle man between Cloudflare and your host, check if your origin might be blocking or rate limiting Cloudflare IP addresses.
In any case, if you have access to your origin logs, it might be a good idea to check them and cross-reference them with the timestamps from when you were served this error.