Context:
When the "use-ipsec" option is enabled on an L2TP Client interface, the configuration and dynamic IPSec peer policy are added to encapsulate the L2TP connection in the IPSec tunnel. This works correctly, the problem appears when disabling an L2TP Client interface, the dynamic IPsec configurations associated with this interface are not deleted in any of the IPsec tables where they were created, therefore a continuous error appears in the LOG indicating a failure in the negotiation phase 1.
Each time the disable/enable process is repeated, new entries are created in the IPsec tables associated with the L2TP Client interface to which the action is applied.
You can see in the image, several entries associated with the same L2TP Client interface, but only one (of each one) is active, the rest of the entries remain because they were not eliminated when the l2tp interface was disabled.