Hehe, I did answer this at the other site, but will answer it here too.

I think he may be about to shed, crested geckos do lose much of their traction (or stickiness of their toes) when they are about the shed. I suspect in a few days he will be sticking as normal to the sides of the cage. It could also be moisture on the cage sides. I do notice after I mist my crested gecko cages they tend to slide more on the sides that are damp.

Below is a holdback from the batch of crested eggs I hatched couple months ago.