I have a Craft installation (v3.7.4) with an Amazon S3 plugin (v1.2.12).
I have an asset field configured to upload to an Amazon S3 volume. IAM roles are properly configured, files get uploaded to S3 - sometimes.
Problem is when I upload a file to a field, it gets saved to the temp location (local temp folder). It does not get uploaded to S3 at first. If I save the entry, nothing changes - no file uploaded to S3.
Weird thing is, if I remove the uploaded file from the same field, and re-upload - then it gets uploaded to S3. So after the file is being replaced it works, otherwise no.
I also tried setting "Temporary Uploads Location" in the Assets settings to S3. Result: Temporary file is written to the S3, but the actual file is not. So it's seems like it's definitely not an S3 issue.
I'm kind of lost, and don't know where to look, so any help would be greatly appreciated!
Edit: I found a similar GitHub issue in the meantime: https://github.com/craftcms/cms/issues/9619