The spell check on this fabulous site is a thing unto itself and, through the simple expedient of offering the next word in its list when it finds a word not on its list, proceeds to baffle and amuse the denizens of this fabulous site.

To me, and without looking anything up recurring would have a connotation of regularity that reoccurring would not. Example: He had recurring dreams of returning to the Navy. If symptoms reoccur see your doctor immediately.

For what it's worth, M-W on line, upon being told to look up reoccur gives a whole list of words starting with re- including reoccur but not recur.

Incidentally, the spell check (AKA Ænigma) does not spot reoccur as a misspelling. It gets like this sometimes. It doesn't like words ending in 's for example.