WebDAV transfers stall for large files stored using S3

I am attempting to download, through a WebDAV connection, a folder containing about 50Gb of data, in files of sizes ranging from very small to 500Mb.

The primary storage is S3.

Through several attempts to transfer the folder contents, the operation repeatedly has stalled indefinitely, after completing transfer for only a few gigabytes of data.

The log reports no failures.

For the record, I have also attempted a variety of similar uploads through the web interface. Such operations repeatedly result in a variety of errors, reported through unhelpful messages, primarily complaining about files being locked.

How might I find the reason for such a serious lack of reliability from my Nextcloud instance?