It just happened to me the same thing. The only way to fix this is to rename the file (I just added one character). Then open it with notepad ++. The code was painted again. Then rename the file back to its original name and it is still colored.
Since then, I have found that if I close notepad ++ without first closing the file, this will happen. Try closing the file first, then closing notepad ++, and then opening the file again.
Simone m
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