You sure you don't have a fret popping up a bit? You could check that with a trusty straightedge.

If that's ok look for a warp where the neck meets the body as in look up and down the neck as though you were peeping your eyes above the deck of an aircraft carrier--loog along the neck from the nut end then the bridge end.

If that ain't it, look to the gauge of bass string you're using.

After that, I'm hooped.