This happened to me with some old grips where the rubber itself had started to perish so no matter what I did (refit with alcohol/hairspray/glue) they would still slip. Only answer was new grips.
Other than that, I would take them off, clean and dry the bars and grips thoroughly, refit with hairspray, then ideally leave to set for a day somewhere dry and warm.
Or embrace it and pretend you're riding a motorbike to Brighton :)
This happened to me with some old grips where the rubber itself had started to perish so no matter what I did (refit with alcohol/hairspray/glue) they would still slip. Only answer was new grips.
Other than that, I would take them off, clean and dry the bars and grips thoroughly, refit with hairspray, then ideally leave to set for a day somewhere dry and warm.
Or embrace it and pretend you're riding a motorbike to Brighton :)