Login loop after installation

Just installed Nextcloud 15.0.0 on fresh Ubuntu 18.04.1 LTS and after initial setup it won’t let me in with credentials I have set up. As advised here: https://github.com/nextcloud/server/issues/13090
I have started from scratch with same result. There is nothing in Nginx error log as well as /var/www/html/nextcloud/data/nextcloud.log.

My Nginx config:
My PHP config:

Any ideas?