Nighthawk App says unknown error when deleting an old device

I recently had a problem with my mk83 after I got it last November, nothing seemed wrong until the internet would randomly be unstable, at first I thought it was because some devices takes more data. So I would occasionally block devices at certain times, however after a while when I tried to to block this one device it would say "unknown error".
So I tried to delete the device when it's off-line but still didn't work and it says "unknown error". Until I completely network resetted the device but it created a new profile that's manageable, while the old profile would just stay. Later I found out it was the with my laptop, network resetting didn't work here. Why can't I delete the offline devices and instead it says "unknown error"?