@Andrew-Brooke55 Hi, welcome to the community. Can I have some pictures of the network map when Deco M4 joined the Mesh, such as: "The issue only occurs when I connect up my M4s to form a mesh...

@mariano20 Hi, can you share a picture or a hyperlink for the Ceiling mount bracket? Considering the speed, I think Deco BE25 should be better than Deco X60....

@afioretos Hi, Can I have the firmware version of the Deco X20? Deco XE75 Pro does support customizing the connection preference, such as Connection Preference: Customize Your Preferred Signal Source...

@marcoin Hi, Thank you very much for the update. Could you please test whether the beta firmware versions here for Deco X50-PoE_V2 help with the current issue: Satellite Deco Units Work Well but...

@OldOne Hi, Thank you very much for the feedback. Please refer to the following workaround: Certain Programs and Service Can't be Loaded Properly on Deco M9 Plus_1.8.0 Best regards.

@LilleLudde Hi, you could just remove the failed satellite Deco without messing with other units: However, if it is the main Deco, you might need to re-configure the new Mesh network. Best regards.