My guess from a simple bit of deduction is perhaps from Objenious/Digimondo. From the Address Space link you shared @BoRRoZ:
0x28/0x29` Germany, Switzerland, China: DIGIMONDO GmbH (0x14)
and this press release:
@kelu28 The reason BoRRoZ made that comment is clear from the link he shared. The information you shared from your console doesn’t match a device that’s Dev EUI was created by TTN. It also doesn’t at least from my reading make it the issue of your problem. But when you set up/added the Device to your console did you input the Dev EUI for your node or did you allow TTN to create it for you? The documentation states it should be something other than x28 which is why BoRRoZ made the comment he did. Just my 2-cents and thoughts though.