As discussed in this comment https://github.com/open-telemetry/opentelemetry-python/pull/419/files/39e0a19f220a20fb5a73d4a5017cfcefb9106c88#r379887377, the behaviour of contextvars in python 3.7 is different from previous versions using aiocontextvars.

The solution as proposed by @condorcet is to apply this patch fantix/aiocontextvars#66