Is this your Listing Agent leaving the house unlocked? If not, then you need to have a conversation with your Listing Agent, they should be able to find out who is leaving your home unlocked, and be able to nip that in the bud.
You need to arrange for your Listing Agent to check on your house for you, to make sure the house is locked up.
If your Listing Agent is leaving the home unlocked, then you need to have a conversation with the broker as they are ultimately responsible.
I wish you the best of luck in your home sale, and hope that Settlement comes soon.
Tamara Stoebe, REALTOR, GRI, e-PRO, CHS, QSC
DRE License #01827461
Prudential Troth REALTORS
1801 W. Ave. K
Lancaster, CA 93534
Cell: (661) 466-6849
Fax: (661) 422-3006