Wi-Fi extender causing slow speeds & intermittent site loading issues (DNS/IP conflict?)

Hi guys, having a weird networking issue on my laptop(Lenevo LOQ):

1. Extender Conflict: When both my JioFiber main router and FTTH Wi-Fi extender are ON, the connection is super slow on one or the other. But the moment I turn off the extender, JioFiber works fine again.
2. DNS Issues: Google and YouTube work, but random sites refuse to load unless I keep switching DNS servers (1.1.1.1, 8.8.8.8, etc.) on my laptop.

Is this an IP conflict/DHCP issue between the extender and router? Should I set the extender to Access Point mode or turn off its DHCP?