Are passwords limited in length upon registration?

I recently registered with an account to post specifically about programming related subjects, too keep it separate from gaming related subjects. I decided to try a password generated by GRC, as can be seen here: https://www.grc.com/passwords.htm

I've got it saved in my password manager, so it's not a problem of having forgotten it. The login form keeps saying it's the wrong password. And I've used them on other sites, no problems with the password-manager cutting them off either.

So I'm going to assume that reddit cuts passwords after a certain length. This may be a wrong assumption.

Does anybody know if this is so and at what length, so I can modify my password?