Caustic does not work properly at all for Android 11 phones. It's built for older model version phones, however I found a loophole that will work.
If you are having trouble loading sample packs and files in caustic with a new phone (android 11), simply take that file and move it to the samples folder in caustic. This helps load drum kits in the beatbox machine,. Next move any sample or loop packs you have to the pcm synth folder.
BEATBOX
Caustic > Samples
PCM SYNTH
Caustic > Presets > PCM Synth