The items can be manually purged from the denylist using the following commands.
clear router <id> l2tp tunnel-selection-blacklist
clear router <id> l2tp peer <ip-address> [udp-port <port>] tunnel-selection-
blacklist
clear router <id> l2tp group <tunnel-group-name> [tunnel <tunnel-name>] tunnel-
selection-blacklist
clear router <id> l2tp tunnel <connection-id> tunnel-selection-blacklist