$500 via Verizon e-gift card (sent w/in 8 wks). Activation of 4G LTE/5G phone on 5G Get More plan req’d. Device must remain active for 45 days. $500 charge back if service cancelled w/in 12 mos or eligibility req’s are no longer met. See vzw.com/bring-your-own-device for details.
I have the same problem as the original poster. It apparently began on Jan. 17, 2012, when Verizon forced a firmware upgrade to the MC524-WR router in my home, upgrading the firmware to version 20.19.8. After being stonewalled by Verizon tech support, I tried an e-mail to ActionTec tech support. They responded almost immediately with the assertion: "When entering the MAC Addresses for wireless devices, it must be done from a computer connected by ethernet to the router. You cannot add MAC Addresses from a wireless connected computer. You should be able to enter a maximum of 10 MAC Addresses to the filter."
I doubted this, since I've had no trouble in the past configuring MAC filtering from a wireless connection, and even now I can do so as long as I don't try to put more than one MAC address in the ACL. However, we dutifully hauled a computer down to the basement and reconfigured it with a wired Ethernet connection to the Verizon router. Lo and behold, in this configuration we could put two MAC addresses in the ACL without problem. Being on a wired connection does make a difference!
So, based on my experience, it seems that MAC filtering can be turned on or off and a single MAC address can be placed in the ACL from a wireless connection, but to put more than one MAC address in the ACL requires a wired connection to the router. This seems weird to me, but it's hard for me to imagine them doing this by accident. They must have designed it this way on purpose.
Anyway, I now have the MAC authentication configuration back the way I want it. I should be OK until the next time FIOS fails and Verizon makes me do a factory reset on the router before they'll believe the problem is at their end.
It would be nice if Verizon/ActionTec would update the user interface on the router to make this restriction clearer, rather than appearing to accept the additional MAC addresses into the ACL and then silently discarding them when the change is applied.