Whenever I select an image and then look at the enlarged version using F11, if I exit that view Organiser deselects the image and defaults back to the first image in the folder. Sometimes it defaults back to the library view. It often does the same thing when using the editor.
This is a very old and relatively frequent complaint about the 'full screen' F11 view. Generally, that behavior is described as the focus getting back to the 'top' item of your view, for instance the top image in the selected folder or even in your whole library.
The reason is that the F11 view works (browses) independently from the main browsing view. The suggested workaround is to start F11 with a reasonable size selection of highlighted files.
Personnally, I prefer to work with albums while having both the organizer and the editor opened at the same time. If I want a full size (100% pixel view), I just open the image in the editor. I have floating documents in expert mode enabled. Double click on the loupe and I am in 100% view with all the editor features available.
The F11 view is useful for scanning and culling, but that's not the only way for that purpose.
To be able to get back in the normal browsing room with the item selected when you quit F11, that means that before goint to the F11 view, you should have a selection (a number of highlighted files, from a folder, a manual selection, the result of a search...)
You get back to your selected file when quitting F11 as intended.
The bonus is that F11 view does open much faster than if you have no selection or a very big one.