Long response time for HTML documents

Hello,

HTML document cached on Cloudflare side (my server isnt ivolved in communication) takes long time to load.
Weight of plain HTML document is ~ 21.9 KB, brotli compressed ~ 5.5 KB.
Wait time (pingdom - London / gtmetrix - London) takes 500 milliseconds! (over 5 times slower than with another CDN provider!).
What is reason of such delay? Other assets not takes that much time.

I have made another test, now it takes over 1 second to connect and over 1 second to wait for Cloudflare response!

Screenshot from Gtmetrix:

Same problem occurs in another tools and physical, desktop devices.