I have 5 raspberrypis running, and they loose connection to one of the decos in the network, not the one they are connected directly to.
When they loose connection the connection to the other clients connected to that deco is clearly also lost.
The connection comes and goes. Sometimes more than 24 hours sometimes only 20 minutes.
It is not always the same client, and sometimes its two of four clients at the same time.

I am so lost and don't know how to troubleshoot any further

Example 
https://drive.google.com/file/d/1PFLf7VFPED_jguTjvX9ys9hujmX5nMJh/view?usp=sharing    

client 192.168.1.97 at deco A 

192.168.1.97 -> 192.168.1.36 fails   ping deco B from client
192.168.1.97 -> 192.168.1.75 fails   ping another client at deco B
192.168.1.75 -> 192.168.1.97 fails   reverse ping
192.168.1.97 -> 192.168.1.83 ok      ping deco A
192.168.1.97 -> 192.168.1.94 ok      ping deco C
192.168.1.96 -> 192.168.1.36 ok     deco B from neighbor client

192.168.1.97 -> 192.168.1.96 ok      ping neighbor
192.168.1.96 -> 192.168.1.75 ok
and everything else I have testet it is ok.

traceroute 192.168.1.36
traceroute to 192.168.1.36 (192.168.1.36), 30 hops max, 60 byte packets
 1  pi0c (192.168.1.95)  3094.284 ms !H  3093.710 ms !H  3093.561 ms !H

traceroute 192.168.1.94
traceroute to 192.168.1.94 (192.168.1.94), 30 hops max, 60 byte packets
 1  deco-M9Plus (192.168.1.94)  55.160 ms  55.265 ms  54.618 ms

My Decos i set up as accesspoints, fast roaming is deactivated.
firmware 1.5.1
ping returns "Destination Host Unreachable"