I had same kind of issue one time with a wifi repeater.

It is quite complicated, i did not understood everything myself, but it is something like that:

The primary routeur give an ip to the repeater, let's call it "secondary routeur" for convenience . So the first device which connect to secondary routeur is provided with the same ip address that the first routeur has provided to the secondary. I don't remember why, but sure it was because my primary routeur was not one of the best.

You can verify this by checking the dhcp client list on the primary routeur, if i remember well, you should see the MAC of your secondary routeur with the same address you get with ipconfig/ifconfig on your laptop, and not see your laptop MAC.

Solution was to give a static ip to the secondary routeur which is out of the dhcp scope of the primary routeur or something like that.

I don't use it anymore and it happened a long time ago, i may have missed some details.

Also, i assume you disabled dhcp server on secondary routeur. If not, try this first.