How do you find out why a GlusterFS peer was rejected?

Question

I tried adding a new peer to my gluster cluster, but it's saying the peer is rejected. I've poured through all of my logs but cannot find any hints.

Magnum-pi and Apple-pi are running gluster 3.7.3 and asgard is running 3.7.6, which may be the problem, but supposedly they are compatible. I can't find a armhf build of v3.7.6 or I'd upgrade those two servers.

Any help to why this is happening much appreciated!

root@asgard:/var/log# sudo gluster peer status                                                                                 
Number of Peers: 2                                                                                                                     

Hostname: magnum-pi                                                                                                                    
Uuid: 08c0b1bf-2858-44ff-a11c-1fc83ebcc54e                                                                                             
State: Peer Rejected (Connected)                                                                                                       

Hostname: apple-pi                                                                                                                     
Uuid: befc6c1b-6d8a-4709-b928-ffc204c8c088                                                                                             
State: Peer Rejected (Connected)