can not add MAC address in Access Control list for RBK752

Hi,

My wifi is Netgear Orbi WiFi RBK752 AX4200.

Hardware Version RBR750
Firmware Version V4.6.5.14_2.0.54

I am setting up MAC address filtering in the Security / Access Control.

Problem Scenario 1 :

i.) Check checkbox  "Turn on Access Control" to enable buttons in "View list of allowed devices not currently connected to the network"
ii.) click "View list of allowed devices not currently connected to the network" to display the list
iii.) click "Add" to display "Add Allowed Device" page and add a MAC address and then click "APPLY" to confirm change

iv.) when adding 38th MAC address

      the system prompt "orbilogin.com didn’t send any data."
      and then the system NOT showing this newly added 38th MAC address

      then after reboot the router, I only can find 29 MAC address, i.e. losing 10 MAC addresses previously added

v.) I then can add back some losing MAC addresses back to the list but problem repeat

*** sometime this kind of problem happened when I have just adding 2x MAC addresses.

Problem Scenario 2 :

vi.) check a checkbox to select a device in the list, click "Remove from the list" and then click "APPLY" to confirm change

vii.) but found the device still exist in the list even performing delete for several times

Query :

BTW, what is the Maximum number of MAC addresses can be added to the list of allowed devices ?

Thanks a lot