Having the same issue on my E+ after buying a 16s. Long pressing until it wants to respond is the only way I can get the wheel on and off, however I find the issue is worse on the old original battery, and goes away when plugged in. I thought the wheel had finally died after a couple months of not being charged but plugged it in and it switched on straight away. I assume it has something to do with voltage or battery degradation and not with the momentary switch. Perhaps someone with greater electrical engineering knowledge than Ican speculate whether a simple button replacement would fix it?