Raspberry Pi Zero W losing WiFi-Connection after AccessPoint restart

Question

I have noticed, that raspberry Pi’s are predictable in losing their Wifi-Connection permanently after the accesspoint was turned off (power off). I have tried multiple raspberrys (10+) and three different vendors of accesspoints and was able to monitor the following behaviour:

Raspberry Pi is losing connection to the accesspoint for an about 40% chance and cannot reestablish it. In an about 60% chance, the connection is reestablished automatically after the ap is powered on again. This means, that usually after 3-4 AP reboots, the connection is not alive on all tested raspis.

Environment

• Raspberry Pi Zero W with Raspbian Jessie
• WIFI-Country set to DE
• Test scenario: AP is restarted every hour by timed switch. Stays of for 5 Minutes and is than powered on again.

Syslog-Output, when raspi is able to re-establish the connection (60% chance)

Syslog-Output, when raspi is NOT able to re-establish the connection (40% chance)

I think: It seems that dhcpcd does not realize that there is no physical wireless connection. An acquired is not even executed. Only a reboot or a restart of the network-stack solves the problem.

Ifconfig – Output (when NOT able to reestablish)

Iwconfig – Output (when NOT able to reestablish)

Wpa_cli status (when NOT able to reestablish)

systemctl status wpa_supplicant.service (when NOT able to reestablish)

I appreciate any help or ideas, that help me to point into the right direction to find the cause of the problem.

Thank you