Hello @quizzy,
welcome to the Nextcloud community 
You’ve posted a request in the support section. Unfortunately you have not completed the required support template. Please edit your post and add as much information as possible so that community supporters have the necessary technical information to help you resolve your issue!
If you really run Ubuntu 18.04. I would recommend you seriously if self-hosting the right approach → please use managed services → 101: Self-hosting information for beginners
Regards,
wwe