There's a known wallet bug we're working on, thus far an annoyance requiring -reindex per that troubleshooting guide; still, we want to solve ASAP so we have the team spun up investigating. We think we've isolated the issue and should have resolved soon. KEY POINT: Your ZEN is absolutely safe, this isn't a blockchain issue and it doesn't involve losing any funds...best practice is always to backup your wallat.dat file / private keys. Sorry for the inconvenience!