That is most definitely an odd occurrence. I haven't encountered this myself on any available firmware. Can you confirm your modem's firmware revision for us? Does this only occur with this feature specifically, or are there any other settings within the GUI that cause the same issue?
Hitron CODA 4582 Device Filtering does not work when you switch between different wifi connections
Currently I have Hitron CODA-4582U , I have 2 wifi names one for 2.4G and another for 5G. When I setup a device to be BLOCKED under Security --> Device Filter, it works first , then if you switch the device within the same modem to use a different wifi connection or direct LAN connection this filter will no longer be working. Any help , I dont want to use the filter under wifi setting because I want to block the device no matter if its connected via wifi or Ethernet (direct connect).