Songbringer's worlds will be shifting in the next update, to be released in about a week. Existing save games will still function fine after the update and all the items you had obtained will still be there. It's just that the overworld and the dungeons will look different than you remember.
If you are in the middle of a world that you want to finish exactly as it is, you can always make a backup copy of your Songbringer directory and use it instead of the Steam version for awhile.
So why is it necessary for the worlds to shift? A bug has been found which is causing the same world seed to generate different worlds on Windows vs Mac and Linux. Fixing this bug will change the seeds which in turn will change the worlds generated. I will be taking this opportunity improve the world generator as well, like making dungeons never right next to each other and preferring ideal positions for the courage refill / save monoliths.
Keeping in mind that with the beta version the game is likely to change often, I suppose this little heads up isn't necessary, but I hope you found it useful.
Cheers,
Nathanael