Yep - that’s almost certainly it. These channels don’t directly line up. Change the wifi channel on tyour new router to something NOT 1. (I’d do 11, myself to get it as far away as you can.
For background: ZigBee and WiFi Coexistence — MetaGeek
2.4G WiFI
2.4G Wifi with Zigbee Channels Overlaid:
See how 14 sits right on top of Wifi 1? Wifi is orders of magnitude stronger than Zigbee and will obliterate any nearby signal if they’re interfering.