Smartthings said here that this issue was fixed with this firmware update.
It’s possible that you need to set it up wired and make sure that this firmware version or later has been applied, then using this link, change your wifi setting by doing a soft reset of your hub (without losing the firmware update).
I got my hub before this update and have never taken it off ethernet because I haven’t needed to, so I can’t say if this will work for sure. Good luck.