Redmine

Hello everyone. I have a problem with changing Priority of some tasks. I can see the Priority field before I edit a task(image 1), but when I attempt to edit the task there is no way I can change this field(image2). I've checked the user's permissions for editing tasks and they're all granted correctly at Issue Tracking.
From what I understood after searching this problem, field permissions must be granted on the Workflow page of the Administration menu, but it seems there's only a Read Only option on my Workflow, as you can see in image3. I don't understand how can I make the Priority field editable, so any help would be much appreciated. Thank you.

My information is:
Environment:
Redmine version 3.4.13.stable
Ruby version 2.4.9-p362 (2019-10-02) [x86_64-linux]
Rails version 4.2.11.1
Environment production
Database adapter Mysql2
SCM:
Subversion 1.9.7
Git 2.17.1
Filesystem
Redmine plugins:
clipboard_image_paste 1.10
recurring_tasks 1.6.0
redmine_agile 1.5.1
redmine_checklists 3.1.5