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Unfortunately, standard load balancer is not supported for Cloud Services Extended Support (CSES). CSES is a parity offering with Cloud services Classic, which also did not support it. As of now there is no update on this to be supported in future.
However, I would request you to submit this feature to Azure Cloud Services - Feedback Community here.
Also, search and follow feature announcements at Azure updates site here.
I hope this has been helpful!
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