It’s probably not worth chasing because it’s rare and probably something to do with the PCB part.
Originally I got someone’s double sided circuit and I moved parts and traces and converted it to single sided, but every time I reopen it it’s back to DS.
If you get this file and click on the PCB it says single side, but if you look at it it’s actually double sided. With just the PCB selected select double side, wait, and then select single sided, and that’s when all the colours change and it’s true single sided. You can save that but it will always open DS visual with SS Insp label.
SingleSideSpeedy3.3 Everything-Ver2-6.fzz (815.6 KB)
I can select everything and deselect the PCB and paste it on another PCB in a new sketch and save that and it stays SS.