Stay connected to specific Wifi which has no internet

I have a Nexus 5 with Marshmallow and another device with a built-in 5.8Ghz WiFi which is used for transfering videos from it. When I connect to this WiFi it keeps telling me, that it has no internet connection and thus obviously disconnecting automatically to find a better one. How do I keep the connection?

Some things I already tried:

• set the freq to 5Ghz only


• delete all the other known Wifis


• manually add the wifi

Unless the connection is stable, I cannot connect to the device with its corresponding app. Are there any apps which could achieve that?

EDIT:

Logcat prints the following when the device disconnects:

12-23 20:29:09.368: D/IpReachabilityMonitor(777): clear: iface{
wlan0/21
}
, v{
4
}
, ntable=[]

12-23 20:29:09.377: I/wpa_supplicant(4270): wlan0: CTRL-EVENT-DISCONNECTED bssid=00:e0:5d:91:1b:ec reason=3 locally_generated=1

12-23 20:29:09.381: D/WifiStateMachine(777): WifiStateMachine: Leaving Connected state

What I found out so far, is that this might be a kernel problem. However, I have not found any references to android in this case.