XF 2.0 URL rewrite - Site upgrade message.

Hi all,

we're struggling with URL rewrite from vB 4 (Advanced URL) to XF2 RC2 friendly URLs.
Old: /<threadID>-<ThreadTitle>
New: /threads/<ThreadTitle>.<threadID>/

We wanted to give a try to THIS resource as XF1/XF2 is pretty same but for some reason we're getting "The site is currently being upgraded. Please check back later." error when we access the old vBulletin URLs.

We're running nginx host machine with PHP 7.1. And yes these two rewrites mentioned in the resource are in place.

Sadly i am not sure how to debug this. It is clear that the rewrite files are doing "something" as we're not getting 404 anymore but where it is getting stuck i don't know :/

Thank you in advance for any clue/help

We're now on RC3 but the situation is same. Could someone put some light in this? I am curious from where the "Upgrade" message is coming from?