That is a strange issue. I'm guessing that some other app is set to download photos in your photos folder. Gallery is then detecting them and displaying them.
The password on the phone?? I don't have one.
I am fairly sure it is no other app on my phone. First time, I was in Germany. Second time in Mexico. Photos are coming from California.
It last until you reboot again. It disables third party apps. If our fellow Ambassador longhiker is correct in the third party app causing this issue, safe mode should help us diagnose the issue.
Long press the power button till the reboot options appear. Than long press the power off. You will see a flyout saying safe mode. Tap it, and your device will boot into safe mode.