My end pin (which is ebony) on my mandolin does the same thing about this time of year most likely due to less humidity. I wouldn’t think you’d have that problem in Florida, but what I did was gouge up the the shaft using a punch or screwdriver to increase the mass that goes into the hole. You can even use channel locks or vise grips to try to give it a knurled effect or anything to make it a little bigger. I tried wrapping it with tape first, but that didn’t work for me. I don’t know if yours is plastic or wood, but either way it should work.
Another option would be loc-tite or wood glue, but that could get messy & could be a problem if you ever wanted to remove it later, so I really wouldn’t recommend that.
The next thing I’m gonna try on mine if it loosens up again is drilling a few holes all the way through the shaft & run some toothpicks or small dowels through the holes with wood glue & let them stick out just a shade until it fits into the hole tight. Don’t know if that’ll work or not, but it seems like it would.