Variations in RFID USB Serial reader detection distance by connected device
I'm pretty sure it does not depend explicitly on the type of device or hub depth on the other end.

The reader sends out an electromgnetic field, which is used to power the chip inside the RFID card, and also to transmit data back to the device. (the card switches a load on and off, which results in variation of field strength over time. The reader detects this.) And there is the USB communication circuit, which is logically independent from the reader circuit. 

It is possible that the field strength heavily depends on the supply voltage of the reader.
Your laptop is quite strong, but when you attach a hub without power supply, it might lower the voltage. 

The embedded Linux box might deliver less voltage since it might be powered by USB itself (like a raspberrypi), and if you attach a display including a hub, which might also be powered over USB, the voltage for the reader can be pretty low. And that causesan cause a weak field an so short reading distance.

Finally, can you measure the voltage on the supply line at the reader? USB allows something in the range 4.7V-5.xV. If you find a relation between voltage and distance, you found the reason.

Or put a hub with own power supply  between reader and next device and check if it's better.