Misbehaviour of asynchronous logic app response when workflow concurrency limit is exceeded

Question

We have a logic app with a HTTP-trigger using an asynchronous response. We'd expect the logic app to follow the asynchronous processing pattern as described here and here. For workflow runs that are immediately started, the logic app behaves as expected:

• POST trigger URL -> returns 202 with location header
• GET location header -> 202
• GET location header -> 202
• GET location header -> 200 -> done

But we have observed behaviour violating our expectation (and common sense :)) when the workflow run is queued in the "Waiting" state instead instead of the "Started" state, for example when the concurrency limit of the workflow is exceeded:

• POST trigger URL -> returns 202 with location header
• GET location header -> 502 with code: NoResponse
• GET location header -> 502 with code: NoResponse
• GET location header -> 202
• GET location header -> 200 -> done

The full error message of the 502 is: "The server did not receive a response from an upstream server.".

The endpoint in the location header of the initial 202 returns a server error (502) when the workflow run is in a "Waiting" state. As soon as the workflow run is started the URL responds with a 202 as expected.

We've worked around the problem by catching server errors on the first poll attempt and simply try again until a 2xx is received. But having clients interpret 5xx errors as 2xx is awkward and should at least be documented. This is a pretty major gotcha for people implementing asynchronous polling of logic apps. Especially because the behaviour only occurs when the concurrency limit of the workflow is exceeded so the problem might not be apparent until stumbling upon the issue in production.

Why do logic app behave in this manner? Is there are more proper solution besides suppressing the 502 error? Also: the documentation I've linked here are pages describing asynchronous responses in general, is there a page describing asynchronous responses as implemented by logic apps specifically?