Intermittent problem with DHCP offering 10.x addresses when configured for 192.x

[Philip Bondi]

Hello to all.

Bell Business Fibe 940/940 Mbps
Router: Asus RT-AX88U Pro, Asus Merlin 3004.388.6_2, Diversion 5.0 blocking list large
AP Mesh: RBR750, V7.2.6.21_5.0.20

Several devices on my home network have intermittently received 10.x addresses when DHCP is configured for 192.x.

Once this happened to Xerox printer which is wired-only, directly through Asus RT-AX88U Pro.

How should I search for more information? I suppose searching logs by MAC address of improperly assigned device?

 

[Tech9]

This means you have 2x DHCP servers on your network. Something is wrong with your settings or connections.

 

[L&LD]

After flashing RMerlin firmware, did you perform a full reset to factory defaults? Ideally, using multiple methods (i.e. WPS Button, Reset Button, and via the GUI, including checking the 'Initialize all settings...' box?

Did you import any old backup config files afterward?

Did you plug in any USB drive that was previously used for amtm/scripts (without first formatting it in a PC to NTFS format)?

 

[bennor]

AP Mesh: RBR750, V7.2.6.21_5.0.20

Several devices on my home network have intermittently received 10.x addresses when DHCP is configured for 192.x.

Check the RBR750, which appears to be a Netgear Orbi WiFi 6 Router AX4200 mesh system. Could be the Orbi's DHCP server is active if it hasn't been properly configured to be an AP downstream of the RT-AX88U Pro.
PS: As others have suggested, also check the upstream Bell Fiber device (if possible) to see if it is not set to bridge mode.
Which specific devices are receiving the wrong IP address? Are they WiFi, wired or a mix of both? If all WiFi then what WiFi network are they connect to? IF wired what are they connected to, the Asus router or the Orbi router/mesh?