@MFKhan 

Make sure the extender is broadcasting two different network names if your networks are named the same, which would cause confusion.

Try changing the 5G channel to something else, factory reset the extender, then set it up again.

@Tony 

My extender has different names for both networks and I can see them both on my laptop. But for some reason its 5G network is not showing up on mobiles only. 

Currently I don't see any setting from where I can update the channels. But I will try doing the factory reset once as per your suggestion and get back to you. 

Strangely enough I connected a new router Archer C60 as an access point to my extender and configured the networks with different names and even they are not reflected on mobiles. 

@MFKhan 

Are you able to see any 5G network on your mobiles? I am wondering if they are capable of seeing 5G networks.

What is the model of the mobile device you are working with?

@Tony 

I already mentioned in my question (see PS in my question) that my mobile phones are dual band and they successfully connect to main wifi 5G network. 

I think the issue here are the 5g channels. It seems that Android devices work on 5g band 4 channels and I don't see any setting to modify channels in extender settings page. 

Can you please let me know if there is any way to change it? 

@MFKhan 

Extender copies the channel of the network it is extending so change it on Wi-Fi source, then set up the extender to it in order to change the channel on the extender.