Display sleeps despite unchecked "Allow Display To Sleep" option on High Sierra
After upgrading to Hight Sierra the display sleeps despite the option "Allow Display To Sleep" being unchecked.
You can try a SMC reset to see if that fixes the issue:
Also you can try deleting Amphetamine’s preferences:
• Quit Amphetamine
• Launch Terminal.app (/Applications//Utilities/Terminal.app)
• Type ‘defaults delete com.if.Amphetamine’ without quotes in a Terminal window and press return
• Re-launch Amphetamine
Hope this helps.