I had the very same issue with a BOOX tablet, where the automated WebDAV synchronization led to files with 0 bytes. My root cause was for sure different, as I’m running Apache instead of nginx. I’m still placing my reply here, as this thread is coming up first in a web search for the issue.
It seemed to be connected with chunked http uploads triggering an Apache bug in its PHP module: 57087 – mod_proxy_fcgi doesn't send cgi CONTENT_LENGTH variable when the client request used Transfer-Encoding:chunked
The bug existed for years and was fixed in 2021. However, it requires a change in the Apache config:
SetEnv proxy-sendcl 1
needs to be added in one of the Apache config files. I placed it in the php config, as that one was the buggy area. After restarting Apache, the uploads were perfectly fine.