Reading file from asset folder sometimes returns "File not found"

On the game, some Android devices cannot read the sound files in the asset folder. If it does happen, it cannot read any of them, but other resource files seem fine. I would say less than 1% of the users experience this but I am yet to find the root cause of it. I am using fmod but this does not seem to be fmod related as it just returns “file not found” as an error.

To access the file, I use:
file:///android_asset/XXX
Since the fullpathforfilename() function does not work on Android for unknown reason

I am wondering if this is something time-related (ie, on slow device asset are not available at the time I try to read them or something like that). Anyone experienced the same thing before?

Thanks

are you using getWritableDirectory()?

No. I am not trying to write, but to read files from the apk package. Does it change anything?