Download fails after some time

First i’d like to point out that i am quite a newbie with nginx and nextcloud, certainly not experienced user. I’ve been runing Nextcloud on my Unraid server via nginx proxy manager using my own domain. It was working well for some time, but yesterday i noticed that suddenly, when i tried to download a file that after a few seconds download stops with “Failed, network error”. I checked nginx error log and i’ve noticed this:

2021/06/17 14:05:53 [warn] 14373#14373: *134587 an upstream response is buffered to a temporary file /var/tmp/nginx/proxy/1/13/0000123131 while reading upstream, client: 77.94.xx.xx, server: nc.xx.com, request: “GET /remote.php/webdav/Share/Grounded.v0.8.1.rar?downloadStartSecret=e7j3ge7zjlc HTTP/2.0”, upstream: “localip:488/remote.php/webdav/Share/Grounded.v0.8.1.rar?downloadStartSecret=e7j3ge7zjlc”, host: “nc.xx.com
2021/06/17 14:05:54 [error] 14373#14373: *134587 upstream prematurely closed connection while reading upstream, client: 77.94.xx.xx, server: nextcloud.xx.com, request: “GET /remote.php/webdav/Share/Grounded.v0.8.1.rar?downloadStartSecret=e7j3ge7zjlc HTTP/2.0”, upstream: “localip:488/remote.php/webdav/Share/Grounded.v0.8.1.rar?downloadStartSecret=e7j3ge7zjlc”, host: “nc.xx.com

can somebody please help me, guide me or anyhow help me? i’d really appreciate it.

BR,
Ziga