Main router drops all traffic when AiMesh node connects or disconnects

I have three RT-AC68u routers in my house. One is the main router in the basement at one end of the house, and two others are AIMesh nodes serving WiFi to the upstairs living areas. Overall the setup works perfectly fine, and while it's old WiFi 5, it still gives us plenty of bandwidth for typical home use.

However, I have come across a problem that is getting more and more aggravating. Whenever one of the mesh nodes goes offline, or when it comes back online, the main router drops ALL network traffic for about 20-30 seconds, including all wired traffic and anything connected to it via WiFi.

Unfortunately, this happens somewhat regularly, due to living in a rural area with a power company that has difficulty maintaining a reliable infrasturcture. High winds, trees, and power lines don't mix. Additionally, working from home means I need a reliable internet connection. Toward that goal, I have a battery backup on the main router (and related networking equipment) and another battery backup on my work computer equipment. I also have a generator for when the power is out for extended periods. However I do NOT have battery backup power on the two mesh nodes. So when the power goes out and the mesh nodes go offline, I lose internet access on my WIRED desktop for about 20-30 seconds until the router decides to pass traffic again. Compounding the issue is that when power is restored (either generator or power company) and the mesh nodes come back online; the main router AGAIN drops all traffic until it syncs to the mesh nodes again. This is incredibly annoying and is just long enough to break my work connections requiring me to log back into everything.

All my routers/nodes are on the latest firmware version, but this issue has been happening for months (years?). Is there some setting in the Asus firmware that causes this? Anything I can change to ensure that the main router still passes WIRED traffic even when the mesh nodes go offline/online?