Using Granular Synth with Stream Cache enabled, Granular Synth will stay silent since it cannot load the sound with Stream Caching turned on.
This was reported and tested in 4.25 (CL-13144385). This was reproduced in 4.24.3 (CL-11590370)and Main 4.26 (CL-13571629)
Currently the granular synth does not support streaming audio files, and stream caching implicitly makes all Sound Waves streaming. However, you can force a Sound Wave to be non-streaming by going to "Loading Behavior Override" and selecting "Force Inline". Doing this will ensure that it can be loaded by the granular synth.
Results: GranSynth stays silent, since it cannot load the sound.
Expected: Gran Synth plays normally.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-93716 in the post.