never stays selected. it keeps reverting back to old drive setting every time i quit the program. This has messed me up greatly and caused hours of lost work. Thinking my stuff is being saved. It also seems to happen even during a session.

I remember when then was never a problem?

Is the drive always mounted when you launch MC the next day? If it's missing, MC will revert to another drive and not automatically switch back.

What MC version?

yes its always on at start up.

Is this specific to a certain project or ALL projects?

This drives me crazy too.  Avid never remembers media creation settings for me.  Its been like that for years.  Ive tried site settings but nothing makes them stick.  We move between different machines on the same network which i think causes the troubles for us.  But the same drives are always mounted on startup.

Avid should remember Media Creation settings on the same computer.

As of now, it does NOT store settings for access on other computers.  You'd have to set each one individually the first time you open a project on that system - but after that, each computer should stick.

However - I, like the OP, have indeed been finding at times with 8.6.5 that this doesn't happen properly.

If it isn't saving for a particular project, try deleting the project's Avid Settings File (.avs). It will rebuild, and that might help.