Unable to Tether Inseego Mifi8000 Hotspot

[Doner005]

Having a weird issue with my Asus RT-AC87R router running the lasest Merlin firmware. I was previously Tethering a ATT Unite Explore LTE hotspot through the usb port of my router with no issues. I have recently switched to Sprint with the Inseego Mifi8000 hotspot and no matter what I do the router will not tether to this hotspot. I confirmed that the hotspot automatically tethers to my laptop and an older netgear router I have. Any ideas on things I could try? I have tried switching between the Usb modem/Android phone setting with no luck.