WN2000RPTv2 installation connection issues

My inlaws have an xfinity wireless router for their condo, which is rectangular shaped. Of course, the router was placed in the far end of the 3 bedroom condo and coverage at the opposite end is weak.

I had purchased this WN2000RPTv2 extender a while ago and now we're suddenly having some problems.

Initial configuration seems to be ok, creating the proper MYSSID_EXT naming.  I can even access the internet and surf.  

However, I cannot access mywifiext.net.  I try via different browsers, direct ethernet connection, IP address, etc. No luck.

I've reset the extender and same results. Ultimately, the extender loses internet connectivity.

I did this twice via manual setup.

(1) Any suggestions on what to do to fix this issue?

(2) With xfiniity, is there a suggestion for a better configuration and extender for this situation?

Thanks.