AiMesh Node Keeps Disappearing

I have an RT-AC5300 as the main node on the 2nd floor, an RT-AC3100 node on the 1st floor, and another RT-AC5300 as a node in the basement. The basement node is constantly disappearing/disconnecting, leaving me with just two nodes. When I reset it, it rejoins the mesh, and shows a full strength connection (based on the web UI - all four bars are lit).

The 5300's on the 2nd floor and basement are two floors away vertically; however, horizontally, they are nearly above/below each other.

I...

AiMesh Node Keeps Disappearing