I've just uploaded 150 png images for a NFT series release and used the following script:

for f in *.png; do
    swarm-cli upload $f \
    --stamp [...] \
    --name $f \
    --content-type image/png \
    --sync \
    --quiet >> hashes.txt
done

To make sure that images are available from the network I also used the sync option. During the upload, for 7 files, I've received the following error msg: Data syncing timeout.

Preferrably, the error msg would tell me for which files it is e.g. Data syncing timeout for 1.png.