Just after posting, I found the following in the related posts threads: https://community.tp-link.com/en/home/forum/topic/591722 After updating and rebooting, the DNS values were preserved so I guess...

Since the latest firmware update (to 1.12.0 Build 221010 Rel.35508n(4555)), the custom DNS servers that I have under Network > DHCP Server are reset to "192.168.1.1" after every router reboot. This...

@Kevin_Z thanks for getting back to me & not sure how my screen name changed. Anyway, I believe this happens when I'm on 5Ghz and the computer automatically switches to 2.4Ghz. The number of devices...