@Munch1 

Can you post a screen grab from the Controller: Map->Topology with Labels ON?

  @Munch1 

How are you powering Drawing Rm and Bureau?  Ideally you would use POE injectors, using a POE switch could cause issues because the etherlink will show as up.

Also, pick an optimal 5.8G channel for your root AP and fix that.

Are you in a region where your channels must adhere to DFS?  (what country are you in)

  @Munch1 

Re-enable 5ghz (but leave 6ghz disabled).  And pick the mid channel available and set it as fixed on your root AP in the 149-167 range.  Try that for a few days.

Hi @Munch1 

According to your description, it seems that the mesh AP might not get a stable connection from the root A. Note that make sure the Mesh AP locate in the coverage of Root AP or other Mesh AP. and for Mesh AP, the recommended signal of Uplink AP is between -40dBm and -62dBm.

  @Munch1 

Absolutely reducing the power does.  There's a hidden SSID on the 5.8G radio that is used for the meshing (there's no secret 5th dimensional radio or anything :) )

Before you physically move the APs around, put the power back to max and set the channel width to 20Mhz.  This will give you the strongest radio signal possible (most watts per hertz).  If that stabilizes things then move to 40Mhz and then 80Mhz and see if that breaks things again.

The problem with meshing is that sometimes the APs farthest apart cannot hear/see each other and will try to talk over each other as a result, causing mayhem with the poor AP in the middle.

Since the system was stable before adding the 2nd hop AP, you can likely fix this by adding yet another AP.  The idea is that in the Bureau you would add a 'slave' AP and cross-connect the two APs there with an ethernet cable, because of the way meshed APs are set up it makes the 'slave' AP appear as if connected to the same switch as the Root AP because the ethernet port of the Master AP is effectively bridged to the ethernet port of the Root.  The trick is now to fix the slave AP's frequency to a different channel than the 'master' AP which then isolates the 2nd Hop AP communications from the Root/Master.  You can disable the 2.4G radio and all user 5.8 SSIDs on the 'slave' AP if you like.