The ongoing oddities with my Mesh Wifi + Uverse RG

Hello Community! Here is my setup:

2 x TP-Link OnHub routers in Mesh Wifi setup 1 x Uverse RG

I have a setup where the Mesh is configured behind the Uverse RG, so I have a double-NAT situation. All of my devices are connected (wired and wireless) to the Mesh and not the RG (except for the STBs, which I believe a require a DHCP connection directly to the RG) so in theory all of these devices should be receiving a 192.168.86.### IP address. My gaming consoles have heartburn when playing certain games with the double-NAT config, so I configured my RG in Pass-through mode which worked beautifully for the first few weeks. The, I started noticing that some of my devices starting receiving IP addresses in the 192.168.1.### range, which is what the RG hands out. I tried various things to fix this problem and keep the Pass-through config in place but I eventually had to break it back down to the Double-NAT config. HOWEVER, some of my devices still kept receiving IP's from the RG's range. I've factory reset everything at least once and still this issue persists.

Has anyone seen this before? Is this possibly a DHCP lease issue? To potentially combat the issue from this angle, I've started reserving IP addresses for each device in the Google Wifi app. I'd rather not have to resort to this as it doesn't really fix the issue.

Please let me know if I've left out any important info. Any input is appreciated, and thanks in advance.