I'm assuming the guitar didn't have this problem & it has developed over the winter.  Also assuming the temperature in your house is relatively the same throughout the year.  So, to my limited understanding, the issue is humidity.  Wood and metal do expand & contract at different rates, but low humidity is what typically can cause the fretboard wood to contract but the frets don't.  This is especially notable in winter months when central heating can dry out the air.  I've read that some people run a humidifier in their guitar room.

FWIW, I've never had that problem & my main Strats, classical guitar & jazz guitar (the ones I use most often on lessons) are always on stands ready to go.  The only time they go in cases is when I'm taking them out of the house (travelling, studio, gig, etc.).  I've got other guitars that stay in cases for weeks or months until I need them for a project.  I take them out, clean them up, change the strings if necessary.  Then I leave them out on stands until I'm done with the project, then put them away for weeks or months.  Again, never had any problem.

So, if you've had it in the case, you might try leaving it out to see if that lets the wood hydrate enough to solve the problem.

But you might want to ask the resident professional GT tech in his forum.

https://www.guitartricks.com/forum/c/30

Hope that helps!