Hello, I use a AX53 in AP mode and have it connected to my modem. I did that before with Netgear and Linksys so the setup was easy. 
But I have a strange problem, all devices that are connected to the AX53 at one point, show up for like 30 minutes in the modem as "active" with a IP.

Even if I check now, my iPhone is listed as active because i connected it for a few seconds to the TP-Link Wifi. 

Usually as soon as I disable the wifi on a device it will dissapear after 5 seconds from active devices on the modem, but with the TP-Link once are active they show up as connected for 30 minutes after the wifi connection is already dropped.

They dont show up as active on the TP-Link as it should be, but it seems to send some information that the device is still active to the modem. 
This oly happens with the TP-Link one, not with the Netgear or Linksys WiFi router. 

Any idea why or how to stop that? 

I tried reducing the WiFi lease time to 1 minute for DHCP on the AX53, but that also did niot change a thing. 

thanks!