Hi,
Thank you for the details!
If the regular results page shows the variation and the WooCoomerce results page does not, then it is very likely that it still does not allow it or somewhere along the way the plugins conflict, that is also possible.
I have tried to log-in with the details, but the username/password is not accepted, can you please check that?
Can you also please add temporary FTP details? I will try to figure out where the product variation parameter goes missing via editing the code.