Parts tracker not recognizing login?

[Chris Dee]

Found the cookie, but it is set to expire at the end of the session. Is there some way to make it permanent?

With the cookie present were you still prompted to login?

Also, when you log in, is the "Remember Me" checkbox checked?

Once the cookie is present it no longer ask me to log in, and I do have the "Remember Me" box checked.

Good. That's how the authentication is supposed to work.
But myBB is still setting the cookie to expire on session close, regardless of the 'Remember Me' setting, which is different to the old forum.