Hello,
did what you said and did service nginx restart. Then again tryed to upload but still the "page not found error"
Then I tryed switching from IPv6 to IPv4 and again tryed to upload. But still error. from log the last attemt you see below.
2017/01/22 23:12:57 [error] 31511#0: *257 client intended to send too large body: 2448488472 bytes, client: xx.xxx.xx.xxx, server: , request: "POST /admin/backup/upload/ HTTP/1.1", host: "vmixxxxx.contabo.h$
Regards, Herman.