Dock does not autohide on restart

A good method involves using a Safe Application listed below >>

Suggest downloading the Application Etrecheck https://etrecheck.com directly from a well respected ASC Contributor. 

Disclaimer: I am not affiliated with nor receive compensation from the Developer.

The application is free or paid from added features. 

Run the application with Full Disc Access ( Security & Privacy - Full Disc Access ).

It will take a Snap Shot -  both the hardware and software.

The Report will Not Reveal Any Personal Information. 

Post back the Full Report - copy and paste - using the Additional Text Icon ( 3rd Icon to last )

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.

Any Third Party Applications that will interfere with the normal operation of the OS, alter, modify, remove or delete or attempt to do so is an invitation for disaster and may require a Reinstallation of the OS.

This includes AntiVirus, Cleaners, Optimizes, UnInstaller etc.

The The Built in Security  is all that is required.

Does this issue presented when booting into Safe Mode. Restart computer and immediately hold the shift key until the Apple Logo appears, then - release.

Safe Mode will do a Repair Disk, clear cache files and eliminate all Third Party software, extension and fonts from loading. The startup will be slow - normal. Once Logged into the computer - run in this mode for 35 - 7 minutes just as long a needed to test if the auto-hide dock issue is tested.

Should the issue not be present in Safe Mode - this could be an indication of a User Account issue or could be a piece of Third Party software interfering with the normal operations of the OS.

To exit Safe Mode - just restart the computer normally.