Neck suddenly needs a shim
 

Hi. I've this (allegedly) Fender body with a Roytek fretless neck stuck to it. The truss rod wasn't strong enough to keep it straight, so i tried unmounting and reverse clamping it. It didn't help, and moreover now i can't setthe action low enough. I don't recall there was a shim in there when i took it apart (weeks ago) so i'm wondering what the issue is, since i did nothing to the pocket or the neck heel. So it must be a mounting issue. What have i done wrong?
(And by the way, any way to check if the body is actually a Fender? There's no serial number or Fender neck plate, though the pickups don't look, and more importantly don't sound, like Krapteks.)

Anyone?

I often use a flat shim for cases like this. It's easy enough to try one and see if it helps.

If not, the next thing I'd try is a reverse shim.

Flat shim as in a shim that covers the whole heel? What do you suggest to use as material? I only have the most minimal tools available, as in a screwdriver and a pair of scissors.

Card stock, like from business cards will work.

I've used layers of masking tape for flat and wedge shaped shims. Business cards or other thin pieces of non-corrugated cardboard also works. I've even used the flat plastic promotional "credit" cards I get in the mail all too frequently.

I also use bass wood of various thickness from the hobby shop for full pocket shims.

We know how to get the action right again but the question is.....
What caused this to happen ?