Four Routers on home network, within an hour or two after RT-AX88U reboot only three?

[nzwayne]

ASUS Device Discovery tool (Windows 10 or iPhone App) shows my four routers on my home network, only though within 1-2hrs after I reboot the RT-AX88U, then the RT-AC86 (Media bridge) drops from the view, but still fully operational. To recover the missing unit to the Discovery Tool, you need to reboot the RT-AX88U.
The setup is...
RT-AX88U - 384.11 (Merlin) - Wireless Router Mode
RT-AC86U - 384.11 (Merlin) - Repeater Mode (the unit that drops from Discovery Tool display)
RT-AC86U - 384.11 (Merlin) - Media bridge
RT-AC66U - 374.43 (John's fork) - Repeater Mode
| Updated to 384.11_2 & later 384.12_Alpha1 and same issue.

Thoughts to what's wrong? Thanks.

| Discovered if the RT-AC86U's are in media or repeater mode and connected via 5GHz to the RT-AX88U, they will drop from RT-AX88U within a short period of time, therefore not seen anymore. If you re-boot the RT-AX88U they come back into configuration. At 2.4GHz, no issues at all...hhmmm.