Ubee is an ISP grade router and are usually leased. While smaller ISPs don’t customize them as much as the major ones, they all take precautions against 3rd party firmware like DD-WRT.
On top of that, the big ISPs like Verizon take extra precautions like restricting specific certain components like the MoCA jack (used for internet and cable) to the ISP firmware so even if you got DD-WRT on your MI424WR (EOL Actiontec), it’s crippled because the MoCA jack is nonfunctional - and some of the later ones like the Rev.I (final MI424WR before the Greenwave) haven’t been as successful as the early Rev.A-D and to an extent E-H. The Greenwave 802.11ac (FiOS-G1100) has yet to see DD-WRT support and will likely come with the same MoCA stipulation if it can even be done.
Get a 3rd party router you like that’s hackable like a TP-Link WITHOUT an integrated modem (Must have eMTA if you have a landline) - it’s a much friendlier solution to change firmware on and you can change the parts out individually.