We're demoing out first wireless mesh using IAP 374 on ver 8.5.0.3
I made sure all the IAPs are on the same version, and joined the cluster prior to being deployed to their current location.
I have 1 AP acting as the portal, feeding 2 points. One of the points has joined the mesh and cluster correctly.
The Other point can be pinged sometimes, and can be seen on the portal when running 'show ap mesh link', but does not join the cluster.
I had factory reset the point and reployed it a couple times, but no luck.
It did join the cluster once, but could not be managed, and shortly left the cluster.
Show log system had the following ( I took 
a screenshot didnt save it as text, my bad).
*edit*
I've just SSH'd to the IAP that isn't joining the cluster over the mesh, here's what I get in it's log system, to provide more info:
Sep 9 07:31:48 nanny[3983]: <303073> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Process /usr/sbin/dhcp-helper [pid 16962] died: got signal SIGTERM
Sep 9 07:31:48 nanny[3983]: <303079> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Restarted process /usr/sbin/dhcp-helper, new pid 17009
Sep 9 07:31:48 cli[4049]: <341004> <WARN> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 cli| Swarm State Change from Startup to Found
Sep 9 07:31:58 nanny[3983]: <303073> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Process /usr/sbin/dhcp-helper [pid 17009] died: got signal SIGTERM
Sep 9 07:31:58 nanny[3983]: <303079> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Restarted process /usr/sbin/dhcp-helper, new pid 17066
Sep 9 07:31:59 cli[4049]: <341004> <WARN> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 cli| Swarm State Change from Startup to Found
Sep 9 07:32:08 nanny[3983]: <303073> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Process /usr/sbin/dhcp-helper [pid 17066] died: got signal SIGTERM
Sep 9 07:32:08 nanny[3983]: <303079> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Restarted process /usr/sbin/dhcp-helper, new pid 17129
Sep 9 07:32:09 cli[4049]: <341004> <WARN> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 cli| Swarm State Change from Startup to Found
Sep 9 07:32:18 nanny[3983]: <303073> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Process /usr/sbin/dhcp-helper [pid 17129] died: got signal SIGTERM
Sep 9 07:32:18 nanny[3983]: <303079> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Restarted process /usr/sbin/dhcp-helper, new pid 17182
<303073> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Process /usr/sbin/dhcp-helper [pid 17182] died: got signal SIGTERM
Sep 9 07:32:28 nanny[3983]: <303079> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Restarted process /usr/sbin/dhcp-helper, new pid 17239
Sep 9 07:32:29 cli[4049]: <341004> <WARN> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 cli| Swarm State Change from Startup to Found
Sep 9 07:32:38 nanny[3983]: <303073> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Process /usr/sbin/dhcp-helper [pid 17239] died: got signal SIGTERM
Sep 9 07:32:38 nanny[3983]: <303079> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Restarted process /usr/sbin/dhcp-helper, new pid 17296
Sep 9 07:32:39 cli[4049]: <341004> <WARN> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 cli| Swarm State Change from Startup to Found
Sep 9 07:32:48 nanny[3983]: <303073> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Process /usr/sbin/dhcp-helper [pid 17296] died: got signal SIGTERM
Sep 9 07:32:48 nanny[3983]: <303079> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Restarted process /usr/sbin/dhcp-helper, new pid 17349
Sep 9 07:32:49 cli[4049]: <341004> <WARN> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 cli| Swarm State Change from Startup to Found
Sep 9 07:32:58 nanny[3983]: <303073> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Process /usr/sbin/dhcp-helper [pid 17349] died: got signal SIGTERM
Sep 9 07:32:58 nanny[3983]: <303079> <ERRS> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 nanny| Restarted process /usr/sbin/dhcp-helper, new pid 17406
Sep 9 07:32:59 cli[4049]: <341004> <WARN> |AP 80:8d:b7:cf:8e:ea@10.134.1.11 cli| Swarm State Change from Startup to Found