Hub 5x DHCP woes

Hello, 

I have a Hub 5x and I run a fair size network with 5 of my own access points running on static IP's (outside the DHCP range) farming out DHCP from the hub 5x router. 

I've had nothing but trouble with DHCP on the hub 5x. It seems buggy and unreliable to say the least.

There's also a terrible bug in the UI that causes the entire DHCP table to get trashed when you delete a reserved IP, which manifests in the router no longer loading the "connected devices" page or the DHCP page, so I then can't manage anything without doing a full reset on the router and starting from scratch. 

I've also had it randomly not assign reserved IP's and just farm out a random one. I've also had it randomly not assign IP's at all (DHCP server crash) and I have to reboot the router. 

I've done some extensive research which leads me to believe these are not unknown problems with the 5x and it leaves me wondering why Virgin are still giving the device to its customers. Surely it's causing a support headache? 

Anyway, I've had enough of the thing and I want to replace it, but I understand you can't, so my only option would be to run by own edge router dealing with DHCP etc.

The problem with that is the 5x doesn't have a "modem mode" and my only solution seems to be just disabling DHCP on the router. However after doing that I've seen double NAT problems where it's still trying to serve IP's despite the DHCP server being disabled (confirmed with packet captures). 

Is there a way that I could obtain a different hub from Virgin that isn't plagued with DHCP issues? or one that at least properly supports a "modem mode"? 

TIA