Postman flows, variables and durables showing "ambiguous" despite input data and durables set

Variables and Durables are both showing ambiguous in a “Send request” block. This is unexpected, because the input block is sending data from its output port. There are also durables set. So would expect data in both of these. What could be going on?

Input block’s output port:

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Ambiguous input variables:

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Blocks in question (look to be connected):

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