try the following: find the folder called com.reactable, it should be located inside your Android's "external" SDCard (often it's physically internal).
Once you have located the folder, enter in it and check the contents of the Soundfonts and Instruments folders.
You should have the files located as follows:
Instruments: contains all .rin files
Soundfonts: contains the default.sf2 file
It might be the case that your "instruments" (the files ending in .rin) are in the wrong folder (this is due to an oversight in a previous release of the application).
If this is the case, move the files inside the appropriate folder.
Let us know if this solves your issue.