I agree with Funk's observation. Either shim in front, bump in the pocket, or the front screws arent pulling the neck all the way down flush. She is a beaut!!!
Loosen the neck bolts while the guitar is still under string tension and see if anything moves, I have actually seen where doing this will pop a neck in proper place depending on what is actually going on. It is also quite possible that there is a shim in there that has moved over time, like a pick or something. Good luck.
I'd opt for the full shim, if the neck isn't mis-aligned. I had this problem on a few guitars, and a shim solved it, and years later, they still play buzz free with the low action I like.
Well, I finally got a chance to take the neck off today. The neck pocket is a total mess! It looks like Edward Scissorhands has fitted it with his eyes closed! Sorry, didn't stop to take pics. The holes in the body have been drilled through twice and there is a bit of movement, hence the 2 additional screws to hold the neck steady! I've put in a shim for now, to at least get the action a bit better. The guitar was so cheap it's not really worth throwing too much at it. I've got the neck level, and just need to fettle it over the next couple of days to get it playable. All of the hardware is good, so I'll probably look to get a body and neck and swap everything across sometime down the line. There was a reason it only cost £155!