Good morning,
Please Configure the policy value for Computer Configuration >> Windows Settings >> Security Settings >> Local Policies >> Security Options >> "Interactive logon: Machine inactivity limit" to "0" which should disable the inactivity lock.
Be aware setting this GPO put's the computer at risk of "Screen Burn" the purpose of screen savers is to prevent the screen from burning an image after hours of displaying the same screen. Ensure you have effective Power management polices to prevent this. These policies can be configured under Computer Configuration >> Administrative Templates >> System >> Power Management
Please let me know if this solves the issue.
Thank you and have a great day!