Is your new wi-fi zone hidden? If it is, then it might behave as you've described. You would need to add
scan_ssid=1 to that network paragraph if it's a hidden zone.
If not, then try again.
- Having remoted into your Raspberry Pi 3B (since it's still connected using the old information)...
Create two paragraphs for the network section, one with the old and one with the new. Try to keep the new SSID and password simple like lowercase letters, numbers and that's it (no spaces).
# Old house
# New house
Then change your wi-fi router's zone/password to what you want it to be (just lowercase letters and numbers without spaces to be on the safe side).