Unable to create a workflow based on mimetype and group membership

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Steps to reproduce

1. Create a tag "deltag"
2. Create a group "autotag" and assign a few users to it
3. Create an external mount that is accessible to the group "autotag" (although this might not be relate)
4. Create a flow as shown below

Expected behaviour

Workflow is created.

Actual behaviour

Regex error from the "workflowengine" app. Maybe this issue belongs in the server?

{"reqId":"ifxsiY2XYeIasD9xp9PR","level":2,"time":"2025-12-17T10:22:11+00:00","remoteAddr":"192.168.21.8","user":"admin","app":"PHP","method":"POST","url":"/ocs/v2.php/apps/workflowengine/api/v1/workflows/global?format=json","message":"preg_match(): Delimiter must not be alphanumeric, backslash, or NUL at /var/www/html/apps/workflowengine/lib/Check/AbstractStringCheck.php#73","userAgent":"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/137.0.0.0 Safari/537.36","version":"32.0.3.2","data":{"app":"PHP"}}

Server configuration

Web server: Nginx

Database: Maria

PHP version: 8.3

Nextcloud version: 32.0.3

If you have access to your command line run e.g.:
sudo -u www-data php occ app:list
from within your Nextcloud installation folder

If you have access to your command line run e.g.:
sudo -u www-data php occ config:list system
from within your Nextcloud installation folder

Browser

Browser name: Firefox/Chrome/Safari/…

Browser version: 124/125/…

Operating system: Windows/Ubuntu/Mac/…

Insert your browser log here, this could for example include:
a) The javascript console log
b) The network log
c) ...

Start with apps/workflowengine/lib/Check/AbstractStringCheck.php at line 73 and reproduce the workflow creation request against the workflowengine API endpoint described in the issue. Trace the mimetype and group-membership inputs to identify the regex failure, then verify that the workflow is created successfully without the reported error.