Hello,
I know it’s been 2 years since this message but I’m facing the same issue and I was wondering how did you solve it? I have my nextcloud behind an nginx server both are running as docker containers. I managed to increase the upload size theoretically (the increased size is showed in admin web interface) by editing .htaccess and .user.ini files but in practice I still can not upload any file more than 1MB. I get “an unknown error occurred”!!