I experienced an issue with Owncloud today where small files wouldn’t synchronize properly. The error message was

The server did not acknowledge the last chunk. (No e-tag were present)

I could not find a way around this issue. Some googling revealed this page on github. It appears I’m not the only one with this issue.

Deep in the thread, asinteg-daehn provided a workaround for the issue. It’s not ideal, but it works. Rename the file to something else, wait for it to sync, then rename it back.

Update:
Currently only found a WORKAROUND: Renaming of all affected files.

• open activity dialog of OC Client
• go to each affected file by double clicking on it’s error message
• rename it by e.g. a prefix “_” -> “_myfile.txt”
• resync succeeds
• now rename it back
• resync should succeed, too

This is very annoying, but a simple workaround.

It worked for me. Hopefully it will work for you too.