Tried the old bootmanager pet you put on this thread and I got the same problem that I could not load any extra sfs.
So I made a new Frugal SlackOff (plenty of space in my Frugals partition sda7) and asked for four sfs to load when prompted during first re-boot.
But only the first three listed actually were running on re-boot.
So I changed the order listed in boot manager and found the new #4 was not loading, just the first 3 (which included the previous #4).
Is it just me - can someone check if more than 3 sfs are loaded and run with the SlackOff bootmanager?
(Hindsight wisdom: In my first finding of this problem, I had set up SlackOff initially with 3 sfs which all were OK on rebooting. Just couldn't get four or five to start-up, except by 'on-the-fly'.
![Rolling Eyes :roll:](./images/smilies/icon_rolleyes.gif)
David S.