On the newer routers the size of the dhcp static list is no longer limited by the size of NVRAM.....it's limited by the total number of characters for all the entries (Broadcom limitation). To add more, you need to use a dnsmasq.conf.add (there are examples if you do a search).
@RMerlin - Since this keeps coming up, does it make sense to add some type of warning based on the char count?
Yep confirmed, I already do validate the max length:
asuswrt-merlin.ng/release/src/router/www/Advanced_DHCP_Content.asp at master · RMerl/asuswrt-merlin.ng
Third party firmware for Asus routers (newer codebase) - RMerl/asuswrt-merlin.ng
github.com