Upstairs mesh is connected to downstairs mesh rather than to main unit.
Once I installed the main unit and a mesh unit upstairs and a mesh unit downstairs, it seems that the upstairs is connecting to the downstairs not the main unit.
@John-Jarreau Thanks for reaching out to us here on the community! To answer your question, there is no way to force the mesh points to connect to the main router, they will always connect to the device that the access point thinks has the best connection. To trick the mesh points to connect to the main router you will want to unplug both mesh points, then plug them in one at a time so you basically force them to connect back to the main router.