This sort of advice certainly isn't for everyone (I'm big on whimsy), but from time to time, I've found that people tend to lose their touch with characters because they're taking them too seriously, or they're super hung-up on only one facet of their characterization or personality.
Do something silly with them. Go on a misadventure. Or, if that's not that character's style, look for characters to interact with that serve as a foil for them, or make a character to contrast them yourself.
Do something silly with them. Go on a misadventure. Or, if that's not that character's style, look for characters to interact with that serve as a foil for them, or make a character to contrast them yourself.