Hello Gaizka Azkona ,

I would first suggest adding Studio to your AntiVirus 'exceptions list' then restarting the PC and Studio.

Also, It would be good to know if you are working remotely on the machine or not.

When you go to Projects- is this set to show all projects?

Now if you go to Open Project- Navigate to the project and open in Studio, 

When closing and restarting Studio, is the available?

If the problem persists,

I would suggest ensuring the project is created and stored on your local machine and isn't synching with cloud storage, such as OneDrive (this appears to be a default setting in W10/newer machines).

Please let us know if this helps.

Thank you very much for your answer, Steven.

I have no filters in the panel, everything is set to "show all projects" and when I reopen manually the project --that I have saved locally-- I can work in it without problems. They just disappear from the list every time I restart Studio... So I don't really know what could it be.

I have One Drive disabled, by the way.

Hello Gaizka Azkona ,

If you navigate to the projects folder 

C:\Users\yourname\Documents\Studio 2021\Projects and scroll down to the project.xml- then open this in a text editor such as NotePad++

Are you projects listed?

If not- close Studio- rename the xml file (just add _old or something)

Now open Studio and create a test project. Close Studio and go back to the new .xml file (not the one you renamed) and open this again and see if you can see the project.

Open Studio and see now if the project is available.

Hello Gaizka Azkona ,

If you navigate to the projects folder 

C:\Users\yourname\Documents\Studio 2021\Projects and scroll down to the project.xml- then open this in a text editor such as NotePad++

Are you projects listed?

If not- close Studio- rename the xml file (just add _old or something)

Now open Studio and create a test project. Close Studio and go back to the new .xml file (not the one you renamed) and open this again and see if you can see the project.

Open Studio and see now if the project is available.

Hello @Lydia. All of a sudden I am having the exact same problem in Studio 2022. I create my projects in the project folder your mention, and every time I close and reopen Studio, two things happen:
- all projects in the Projects view disappear from the list and I have to manually open them: 
- my custom project templates that I had created and added to Setup/Project templates (I had also selected one of those custom templates as default), disappear and Studio reverts to the original Default project template. And I need to also reconfigure that setup every time. 
I tried renaming the projects .xml file as you suggested, but when I close and reopen Studio, a new projects xml file is not created. 
By the way, when I open that file I see the list of the original projects that were opened in the Projects view before this problem started to happen. I am not the only one who is experiencing this problem, but it seems to have come out of the blue all of a sudden. 
Any ideas what can be causing it and what the solution might be?
Thanks.