We just did a major platform upgrade recently and S3 Uploads stopped working:

Unable to create directory. Is its parent directory writable by the server?

I was almost giving up tonight when I had no more hair to rip off my head, but in a desperate move I noticed the STREAM_IS_URL flag at stream_wrapper_register:

This, of course, clashes with our php.ini directive which disallows such requests.
The thing is: PHP fails completely silent when this is turned off, so I couldn't find the root cause fast enough.

I just enabled allow_url_fopen and it is now back working as it should.

It would be great to insert this as a known caveat at the README for future developers.

Thanks for this amazing plugin!