RGB LED Controller V4 lose Wifi connection

[imsturmdernacht]

Hello, my problem is something off topic. But I do not know who else to contact. I use this RGB LED controller with a FritzBox 7490 router.

https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTmYm5se9wGGVujMqABdUq58AL33dg_YG2nAVHyuGVwxw1Tfy4PHQ

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3 of these controllers are shown as V3 in the MagicHome app. 2 of these controllers are shown as V4 in the MagicHome app. These 2 V4s lose their wireless connection at regular intervals and I do not understand why. I use a fixed channel 6 with WPA2. No special characters in the SSID or similar. I have now also connected as a workaround an old TP-Link AccessPoint. This AccessPoint is only for these 2 controllers and has its own WLan and with this AP everything is fine. Why are the V4s making these problems with my FritzBox and where is the difference to the V3?