i had that exact same issue,

I actually thought i must have had a flat and hit the hump. but it may have gone down cos i hit the humo unsure,

Anyway same as me i spun it up on the machine and it was way out

basics are Jonny get some wood 2 by 1 and smack it hard inside the rim and it will retake the shape, you can have it done proper but its gonna be weaker in that area.

I actually bought a new one in the end i have the poorly one still in my garage if ne1 wants to buy it 100 quid. Still works ok

I also had major issues with Balancing the Gt1s really out lots of weights never felt good wheel always wobbled basics are crap i thought