@Eragon . Probably, because in AP mode the device has a limited features available. Check this article. Also according to this FAQ (Q7/A7) - while wireless routers support OneMesh only in router...

Make sure that the extender SSID, to which you connecting the camera is different than the base modem SSID. Changing the ISP should not causing that issue.

@YazanMajadba You can use the AP mode of AX50 to achieve that.

While it's desirable to place the TL-WR845N half of the distance between AC750 and the room where your computer is, the only way to determine if that will work as desired, is to try it. You can use...

@Dinno Try positioning the device closer to the main router. 5GHz band is more susceptible to distance than the 2.4 GHz. If that persists use the web GUI of the device via browser.

Try opening UDP ports 500 and 4500 in the destination device. Also make sure this is enabled: