Okay, so I've cracked it now!!
What you need to do is download sonic lost world as a .3DS file, not a .CIA file.
Then you need to generate an "ncchinfo.bin" file from SLW (using 3DS simple CIA converter) to generate XORPADs in RxTools.
After you've generated the said XORPADs, you will need to put them into the "xorpads" folder of the 3DS simple CIA converter folder.
Now run the 3DS to CIA conversion. You should get the Sonic lost world CIA file which should now work.
That's how Sonic Lost World worked for me, anyways...
I finally tried your method and it works !
I have an old 3Ds XL 10.3 EUR and used an EUR 3ds SLW.
Thank you !






