Is there settings with error's templates?

In old version of haproxy 1.8 was

HTTP/1.1 302 Found
Location: https://localhost/

In new version 2.1 it is

HTTP/1.1 302 Found
location: https://localhost/

with “l” in lowercase

Is it possible to revert it back to Uppercase “L”?

If you have a bogus client that breaks otherwise, yes, you can workaround this client bug with the bogus client features that have been introduced for this use-case. Something like:

global
 h1-case-adjust location Location
default
 h1-case-adjust-bogus-client

Also see h1-case-adjust and option h1-case-adjust-bogus-client.

Thank you! Works fine now.