This problem is really easy to replicate. I have an Archer VR600 and two TL-WPA8631P (v3.0) sets all connected together via OneMesh and PowerLine.  You can check this old post for a detailed description of my network setup with diagrams: https://community.tp-link.com/en/smart-home/forum/topic/269192?replyId=614554

The VR600 is running the latest firmware: 1.4.0 0.9.1 v009e.0 Build 210826 Rel.42166n

Both TL-WPA8631P units are running the latest firmware: 3.0.0 Build 20210514 Rel.45003

The VR600 plugs into TL-PA8010 for the PowerLine backbone of my network. I also have two TL-WPA8631P (v3.0) units which form the OneMesh network with my VR600, as well as providing wired LAN access to my PowerLIne network.

If I reboot my VR600 (or there's a power cut), it "loses" the two TL-WPA8631P units in the OneMesh display on the web interface. The only way I can rebuild my OneMesh network is to log into the web interface of both TL-WPA8631P units and remove them from the OneMesh network, then physically disconnect the power to the VR600, wait a couple of seconds, then power it all up again. Then it can "see" the TL-WPA8631P units & I can add them to the OneMesh network.

This problem is not linked to the new firmware, as it was happening in exactly the same way on the original firmware for both the VR600 & the two TL-WPA8631P units. It still happened when I upgraded everything to the first set of firmware updates, several months ago - so it has always been present, in every version of the firmware for both the TL-WPA8631P & VR600 units. Apologies, but I just haven't had the time to report it.