Comment 11 for bug 1983307

This error was caused by this line in KF5 Attica code:
https://invent.kde.org/frameworks/attica/-/blob/dde032d415e26a87f900eb6f0131f5114f0e72f9/src/provider.cpp#L1724

User-Agent header was set to UTF-8 value, "knewstuff-dialog/1.0 (+Вход в систему)" in my case.
It's not valid according to HTTP standard (as I know), so HTTP server breaks connection.

(See also: https://stackoverflow.com/questions/10384741/is-a-unicode-user-agent-legal-inside-an-http-header)

Commenting this line solves issue for me.