Thanks for taking the time to answer Lili.
The other day I’ve been rescaling the origin server that caused the 521 errors you noticed - most of the time the server is up and running fine.
Apart from that connectivity is just fine, no firewalls etc. in the way.
I’ve checked the cache, it’s working, dynamic pages are not cached, static content is cached.
The slowdown comes from the fact they are cached at Ashbourn USA, at not Budapest HU (closest CF point of presence for all of my target audience, all of Hungary)
Since origin server is at Falkenstein DE, packets have a suboptimal route, from HU to USA to DE and back, instead of HU to HU-BP to DE and back.
And I don’t get why? Caching at the right edge server would be the core task for the CF cache.