Cyberduck, which is a ridiculously awesome file transfer and storage browser application, has a little quirk that caught me off-guard. When uploading to Azure, it writes append blobs by default instead of block blobs, and personally, I only need block blobs.
There’s no actual setting in the app, but after a bit of help, and reviewing this link and this link, the solution is to create or open the file at:
users\{me}\appdata\roaming\cyberduck\default.properties
or
/Users/{me}/Library/Group Containers/G69SCX94XU.duck/Library/Application Support/duck/default.properties
Add the following line:
azure.upload.blobtype=BLOCK_BLOB
Files will now be uploaded as block blobs.