Internal Server Error when trying to add several subtasks with quick add magic

Hi!
I am trying to improve my vikunja-experience and use more of all the possibilities vikunja has.

I would like to create entire workflows as projects or tasks.
Initially I listed the 12 subtasks in the description, but since most of them are recurring tasks, the subtasks were still all checked the next time I opened the task, meaning I always have to uncheck them one by one, which I don’t like.

So now I’m trying the following approach:
I create the task as a project, and the subtasks are now all individual tasks within that project.
Since, in a workflow, each subtask is a successor to the previous one, I tried using the “quick add magic” feature and indented them with two spaces, but I keep getting an “Internal Server Error.”

Can you help me solve this problem?

EDIT:
It is an database-problem (“database is blocked”).
Seems that sqlite is not capable to add 2 subtasks at once.
Perplexity recommended to use PostgreSQL or MariaDB.
I will try this.