As Vaughan said. It is an oxidiser - if there are organics common to its solution to oxidize, it may be lacking in pep to do all of what you want it to do when mixed into the cyanotype solution.

I usally add amm bi/dichro drop wise to fine tune the contrast resonse after I mix the basic chemicals and expsoe a step wedge to see what the sensitivity and contrast the fresh batch is exhibiting.
So even if it is weakened, just add a few more drops in, if the mix looks like it needs it to mate to the response of the large format/ enlarged negatives you want to work with.