Follow-up: it finally stopped at 6.9GB! But only 2 volumes were actually uploaded to S3...
6.9GB 01:13:58 [195.4KB/s] [=======================================> ] 99% ETA < 45sec
Thread-1: Uploaded 26042368/26214400 bytes
Thread-1: Uploaded 26181632/26214400 bytes
Thread-3: Uploaded 24788992/26214400 bytes
Thread-1: Uploaded 26214400/26214400 bytes
6.9GB 01:14:01 [303.2KB/s] [=======================================> ] 99% ETA < 45sec
Thread-1: Uploaded chunk 8 at roughly 26083.8271029 bytes/second
Thread-1: Upload of chunk 8 complete
6.9GB 01:14:04 [212.2KB/s] [=======================================> ] 99% ETA < 45sec
Thread-3: Uploaded 24928256/26214400 bytes
Thread-3: Uploaded 25067520/26214400 bytes
Thread-3: Uploaded 25206784/26214400 bytes
6.9GB 01:14:07 [175.7KB/s] [=======================================> ] 99% ETA < 45sec
Thread-3: Uploaded 25346048/26214400 bytes
Thread-3: Uploaded 25485312/26214400 bytes
6.9GB 01:14:10 [150.2KB/s] [=======================================> ] 99% ETA < 45sec
Thread-3: Uploaded 25624576/26214400 bytes
Thread-3: Uploaded 25763840/26214400 bytes
6.9GB 01:14:13 [132.3KB/s] [=======================================> ] 99% ETA < 45sec
Thread-3: Uploaded 25903104/26214400 bytes
Thread-3: Uploaded 26042368/26214400 bytes
6.9GB 01:14:16 [119.8KB/s] [=======================================> ] 99% ETA < 45sec
6.9GB 01:14:19 [83.8KB/s] [=======================================> ] 99% ETA < 45sec
6.9GB 01:14:22 [0.0B/s] [=======================================> ] 99% ETA Stalled!
Thread-3: Uploaded 26181632/26214400 bytes
Thread-3: Uploaded 26214400/26214400 bytes
6.9GB 01:14:25 [75.5KB/s] [=======================================> ] 99% ETA < 45sec
Thread-3: Uploaded chunk 6 at roughly 22478.6619143 bytes/second
Thread-3: Upload of chunk 6 complete
Done waiting for the pool to finish processing
Deleting /tmp/duplicity-HTVBro-tempdir/mktemp-9a2Ll7-3
Forgetting temporary file /tmp/duplicity-HTVBro-tempdir/mktemp-9a2Ll7-3
AsyncScheduler: task execution done (success: True)
AsyncScheduler: active workers = 0
Releasing lockfile /home/andrew/duplicity_hashes/SurfacePro4Documents/lockfile.lock
Removing still remembered temporary file /tmp/duplicity-HTVBro-tempdir/mkstemp-6YdDqP-1
Removing still remembered temporary file /tmp/duplicity-HTVBro-tempdir/mktemp-fiG4h1-4
INT intercepted...exiting.