My $0.02...
I believe your D-55 would have a nitrocellulose lacquer finish.
The back of the neck of a couple of my dreads will start to feel a little sticky... not so much soft, just not slick, when I play for any length of time. Somewhere, I read that this was likely a rxn between my body chemistry and the finish. I just wipe the back of the neck down with an old (clean) dry cotton diaper when it starts to feel that way... and then can go on playing. I also am careful to wipe down those guitars before I hang them up after playing. Don't know why all the necks on my dreads don't react this way... they are all NC finishes. I do notice that its a little more of a problem when the humidity or temp are higher... presumably because more sweat/oils are coming off my hands. Apparently, some peoples body chem is more likely to react than others...
The other thing to watch, if its just a patch, is REAL softening of the lacquer. When my D-35 was new (a LOOOONG time ago), I stored it in its (also new) hardshell case. Apparently, the plasticizer from the foam padding under the neck softened the finish in a spot the size of a half dollar right over the neck support. I tried leaving the guitar out (for nearly a year) to see if the lacquer would harden back up... and it never happened. I finally just scraped the soft lacquer off with my fingernail and a soft cloth... and have had a bare spot on the neck for the last 30 years. Probably not the wisest thing to do... but I plead youthful ignorance. In retrospect... I probably could have sent it back to the factory for warranty service... a little late for that now, I think. Just one of its (many) beauty marks that make it mine...
So, if its just a little "stickiness" when you play, wipe it down and go on playing. If the finish is really getting gummy and soft (if you fingernail leaves an impression), I would seek advice from a good luthier.
As I said... just my $0.02. YMMV.
Dave
Oh... and welcome to LTG!