The access points can mesh with either an encrypted connection or unencrypted connection. With an encrypted connection all access points need to have the same encryption key, otherwise they won't mesh. When you turn off "AP Mesh" these keys get scrambled, to prevent meshing. This is why "Mesh Encyption" remains enabled when "AP Mesh" is turned off.
A wireless repeater requires meshing in order to connect to the network. If AP Mesh is turned off, it will go into "orphan" mode asking for help from a surrounding access point to connect to CloudTrax. It may be able to report into CloudTrax as an orphaned AP, but it will never be able to establish a proper mesh connection. Without a proper mesh connection, client devices won't be able to connect through these repeaters. It is not recommended that you turn off AP Mesh if you are using wireless repeaters.
In most cases you should leave AP Mesh turned on. If you believe the mesh may be causing instability or looping events on your network, and you do not have repeaters, turning off AP Mesh might help.