Symptom:
ASA allows some non-cisco ikev1 clients to use an assigned IP without going through address assignment.  This means that the used IP is not marked as in-use in the address pool, which means that it may be assigned to another client that does go through address assignment.  In this case, the conflict is resolved by kicking out the oldest IKEv1 session using that IP.

Additionally, the ASA doesn't check that the client actually opens a tunnel matching it's assigned address.  This can lead to the same conflict mentioned above.

Conditions:
Mixture of cisco and non-cisco ikev1 clients in use

Non-Cisco IKEv1 client uses assigned address without going through address assignment, or ignores address assignment result.