Hoping someone else can verify this, but it appears that the Withings app isn't sending passwords with spaces correctly to the device.
tried on two routers, first had a password similar to "this is a password" and the second had a password similar to "thisisapassword" - I was able to connect on the second, not on the first. Multiple reboots, resets, etc same.
Changed #2 to "this is a password" and it failed.
Added a guest network to #1 with "thisisapassword" and it worked fine. Tried to connect to original (which is also broadcasting the guest) and it fails.
So pretty sure the things do not work with spaces in a password.