Bug: can't login via Cloudflare proxy

[devops-from-root]

• lattest Carnet app from fdroid v0.25.1;
• lattest Nextcloud app from GP v3.30.8 (app from Fdroid have same result);
• lattest Nextcloud Hub 9 v30.0.5 (with any others version of Nextcloud server same result).
• Android 11 (10 and 12 same result)

I've installed the application, connected to the account manually entered the login and password. Carnet synchronized notes. Changes on the server are loaded into the application. Changes on the android also end up in the cloud. All works whell.
After that, I connected dns protection against Claudflare. Only proxyng DNS without anything else. So I worked for more than a month, synchronization works well.
Then, I needed to connect Carnet on another Android. And I didn’t have authorization in my application. Carnet app offers to check the authorization data. On nextcloud logs I've got:

Error no app in context
BadRequest
The expected file size is 60289744 bytes, but from the Nextcloud application client, 60129280 bytes were read and written to the store. This could have been caused by an error when transmitting data on the sender's side or a problem in the server-side storage subsystem.

And after some time

Warning | no app in context | Login failed: username (Remote IP: X.X.X.X)

I started checking on the already configured Android. Synchronization is going well. On Settings -> Sync with cloud storage -> Change Credentials I click on the CONNECT button and get an error that the credentials are incorrect. The same as when connecting on another android.
After all of this, I turned Cloudflare off. And now login in Carnet app work whell.