I have run into the same issue with Resolve 12.5.4, 5.5 and 5.6 on more than one system and it's driving me crazy. Can't remember if earlier versions did this but man is it frustrating and time consuming. I have a few projects with a ton of bins and sub bins and no matter what I do, every time I save the project and come back to it later all the bin tabs are turned open and they have to be manually closed.
So I have one in particular that has about 25 Root Bins and within each Root Bin there may be up to 3 levels deep of sub bins. So I open up the project and every tab is turned open which reveals every bin that's in the project. This is even after I had previously saved the project with only the tab of one root bin and the next sub bin(s) I'm going to add media or timeline(s) to the next time I launch it.
I now launch Resolve to add the next batch of media and/or timeline(s) and once again every tab is turned open and there's a mile long list of bins that need to be closed. Even worse when I close them all in the Media Window and then go to the Edit Window they are all still tuned open and must be closed there once again.
Is there a setting or preference somewhere that will stop this or is this just a bug.
All I can say is it's bloody annoying especially on those days when I must quit and reopen Resolve several times, like a movie.
"MY MEDIA/PROJECT MOTO: If you think three copies of your media or project are enough.
Take a moment to place a value on them and then maybe add two more.
Hard Drives are now stupidly cheap. A RE-SHOOT AND YOUR TIME AREN'T."