WNDR3700/3800 can't use tftp failsafe mode


I own a handful of WNDR3800 APs and it has become impossible to enter failsafe¹ mode for one of them. The AP is working fine otherwise, but it's a bit annoying. Has anyone had that issue?

¹ See https://openwrt.org/toh/netgear/wndr3800#recovery_flash_in_failsafe_mode

edit: sorry might be the wrong sub.