AEBS and HH3 DNS errors

I have a Homehub3 and an airport express base station 5th gen. An ethernet cable connects them from the HH port 1 to the AEBS small circle port. The AEBS extends the wireless network around the house. IP addresses are assigned fine but DNS and router addresses are often allocated as 192.168.1.2 instead of 192.168.1.254. If we change these manually on all devices we can connect. If I turn the AEBS off, the problem rights itself. I wonder if there is some conflict between the HH and the AEBS that is causing this. I am looking for a simple fix for this as I am not at all computer literate so, if buying a moden to replace the HH is the best solution, I'll do that rather than spend the same money on someone from the local computer shop coming out here and spending hours trying different configurations and not fixing it!

 

I've just checked and it's already in Bridge mode

 

Solved

By trial and error (unplugging another wireless extender), I seem to have fixed the issue which was most likely caused by interference from this other extender. Thank you for your help.