Maple Fretboard Finish Cracks

I am working on a partscaster with a maple neck (maple fretboard) that I purchased unfinished then I finished with nitro. After about 4 double coats I did a knock down sanding with 400 grit. Then I did 4 more double coats and started with 800 grit wet sanding. With the wet sanding I had some cracks appear in 5-6 frets. What would have caused this and what am I looking at to remedy the situation?

Water got under your frets and seeped into the fret slots

Water got under your frets and seeped into the fret slots

Colt...thanks...makes sense. Is it better to wet sand this area with naptha or no lube at all? Any experienced suggestions? Also, to remedy the cracking I guess I need to make sure the water dries out then sand out the cracked areas and re-shoot huh?

Its always something isn't it?