Long-running functions do not output any logs?

We've observed that edge functions running longer than approximately 17s do not output anything via console.log (or other logging systems we've tried, like Axiom)

The function otherwise does complete! e.g. database calls at the end of the function fire successfully. Just not console.log output.

Additionally, this only seems to show up at the 17s mark.

This repro-repo is a freshly bootstrapped create-next-app using appdir + edge runtimes

Getting started

Note that this bug only shows up on Vercel, not locally! But just showing local steps for completeness.

First, install dependencies:

npm install

Then run the development server:

npm run dev

Then make some requests to our three sleepy test endpoints, and watch your server logs.

• all 3 of these tests result in a 200 OK with the expected data. So the good news is they still technically work
• but 2 out of 3 of the tests do not produce any console.log output at all. That's the bad news
• `/test2`` specfically produces a "Error: Network connection lost." error on Vercel, which doesn't happen with the other two
• all 3 tests behave consistently over dozens of test runs (as of 2023-09-19)

POST /test -- 20s -- works, but no console.log output (HTTP streaming, 20s long sleep)

curl -s -X POST http://localhost:3000/test

GET /test2 -- 22s -- works, but no console.log output (RESTful reply, 22s long sleep)

curl -s -X GET http://localhost:3000/test2

GET /test3 -- 10s -- works and does produce console.log output (RESTful reply, 10s long sleep)

curl -s -X GET http://localhost:3000/test3

Testing against a Vercel deployment

hostname="https://mydeployment.vercel.app"; curl -s -X POST $hostname/test; echo; curl -s -X GET $hostname/test2; curl -s -X GET $hostname/test3