Stain on concrete

That looks like rust/iron stain. Some type of acid will clean it if it is rust. Vinegar, ascorbic acid, muriatic acid diluted 2 or 3 to 1, etc. Always add acid to water.
 
I suspect that it might come back if something metal is rusting. Possibly some rebar or framing iron.

Looks rusty at the top near that blue tile.

Looks like rusty water is seeping out and running down the control joint.
 
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