I have the AX1800 Flint router and just updated to beta 4.0.1 and find the same problem as the OP re the Kill Switch functionality. In V3 the kill switch worked as logic dictates - ie if the device is excluded by mac or IP then it is not affected by the kill switch. Perfect logic - and it worked perfectly.
After the upgrade to V4, even though the device is excluded by mac address, that device is completed blocked by the VPN kill switch. That is not logical and entirely stupid!
Please change back to the logic you applied to V3. A working and logical VPN Kill Switch is an essential tool.