@InabaYuu 

Hi,

Was your RE3000X blocked right after you connected it to the student network or was it working for days or even weeks before it got blocked?

If it worked for a while, then my guess is that the network administrator one day performed a scan with a Wi-Fi scanner/analyzer software (or phone app) and found there is a new network device broadcasting that isn't one of his own.

Unlike a network adapter a repeater will broadcast an additional wireless network(s). Even if the SSID is hidden this network will be shown in Wi-Fi scanner/analyzer software together with the MAC addresses of the wireless radios. (the picture below illustrates how a dual-band wireless repeater with hidden SSIDs shows up)

Based on these it is usually easy to find out the MAC address with which the repeater is connected to the main network and this MAC address can be blacklisted by the administrator in the network controller.

As far as I am aware TP-Link devices don't allow the MAC address(es) of the wireless radios to be altered manually by the user. This feature only exists for the (wired) WAN ports of wireless router models.
 

  @InabaYuu 

Hi,

if your network extender's front router is a school-managed router, if so, the network administrator may recognize that your network extender is not a common device and prohibit access to the network, you can try to wired connect to the front router.