GitHub Actions step is hanging until timeout

Problem

Describe the bug At some point, a GitHub Actions step stops producing output and hangs until the workflow is terminated by timeout. You can see the output stops being produced if you actively watch the job output in the browser. If you try opening an already hanging job in the browser, the step output is not displayed at all: the ">" sign next to the step is not visible and the icon next to is is a spinning yellow circle. The output becomes available once the workflow is terminated. Here is an example of one such run. Here is the log with timestamps: boost_log_gha_hang.txt.gz I'm sure the processes running in the GHA step are not hanging (this is just a C++ compilation process, which does succeed normally). This problem seems to be not unique to my setup, there are other reports as well. In my case it happens most often with macos-10.15 runner, but I've also seen it happen with ubuntu-20.04 runner. To Reproduce At the moment, this reproduces quite reliably by running the workflow on my Boost.Log repository (git revision boostorg/log@2f058c6d8c3867471d0973b6f57127b5076a4f7f). I intend to try working around the problem (e.g. by disabling the offending runner), so this may not stay reproducible in later revisions. Expected behavior The runner should not hang. Runner Version and Platform I'm using the free runners hosted by GitHub.