Some POST requests in a small subset of Chrome browsers return 411 error for some reason. The server's endpoint returns 200 in most of the other devices also using Chrome. We're using a load balancer in AWS and our backend is .NET. What could possibly be the reason for this?
Edit: I noticed this only happens when there is no body in the POST request. It could be the browser omitting Content-Length: 0 in the request headers for some reason. But what could be making the browser do such behavior?
After experiencing the same problem in both Chrome and Edge across two different websites, I think I have the answer:
The problem appears to be BitDefender antivirus.
If I disable BitDefender protection, the post requests succeed.
Bizarrely, if then re-enable BitDefender protection, the issue doesn't come back.
After stumbling across the solution, I found a few references to people having the same problem: https://community.bitdefender.com/en/discussion/88573/status-411-length-required-during-browsing https://support.mozilla.org/en-US/questions/1344632