EDIT: we had issues impacting the FM call, but it was not a timeout one. So keeping as-is as it works fine for now.
When completing an upload, the FileManager call is done with a big timeout (21,600 seconds). It is so to handle big files.
Let's see what can be done to get rid of that huge timeout.
If an error happens at the call to the FileManager, Drive will retry 60 seconds later. But then, as the batchId was used once, it has been automatically deleted: so a new upload will start from ground.
The remote client should make use of the X-Batch-No-Drop header to prevent the batchId purgation after its first use. And a manually cleanup should be done only when the upload is fully done.