I upgraded to 16 a few days back and ever since synchronization between server and clients stopped working.
I am getting loads of log entries like this:
2019/05/13 17:17:52 [warn] 42731#0: *41678119 a client request body is buffered to a temporary file /var/cache/nginx/client_temp/0000008497, client: 179.34.144.121, server: my.nextcloud.com, request: "PUT /remote.php/dav/uploads/januseraccount/3278489535/00000002 HTTP/1.1", host: "my.nextcloud.com"
2019/05/13 17:18:07 [error] 42731#0: *41678119 upstream prematurely closed connection while reading upstream, client: 179.34.144.121, server: my.nextcloud.com, request: "GET /ocs/v2.php/core/navigation/apps?absolute=true&format=json HTTP/1.1", upstream: "http://127.0.0.1:443/ocs/v2.php/core/navigation/apps?absolute=true&format=json", host: "my.nextcloud.com"
2019/05/13 17:18:17 [error] 42731#0: *41682013 upstream prematurely closed connection while reading upstream, client: 179.34.144.121, server: my.nextcloud.com, request: "GET /ocs/v2.php/core/navigation/apps?absolute=true&format=json HTTP/1.1", upstream: "http://127.0.0.1:443/ocs/v2.php/core/navigation/apps?absolute=true&format=json", host: "my.nextcloud.com"
This is with a new php version 7.1, and everything was working before the upgrade.