Files slow uploading to server via Cloudflare proxy

When the domain is proxied by Cloudflare all upload to server processes extremely slow down.
When I turn off the proxy and leave DNS only, everything works well. I tried to create different page rules, WAF rules, and configuration rules pointing to the URIs that perform file uploading, but nothing helped. Please, what do I do wrong?

I’m facing the same problem where using Cloudflare’s proxy slows my uploads way down, but switching to DNS only fixes it. I’ve tried tweaking settings, but nothing’s worked. Anyone else dealt with this? How did you solve it? I’m looking for a way to keep using Cloudflare without the lag.