Left many free storages,but couldn't download anything

View attachment 2020 I'm using Oppo Find 7 and I'm new to android.I'm facing a funny problem I think.My phone is still having a total of 40GB free memory to save or download apps,musics or pictures,but when I wanna download something,it keep saying.that I don't have.anything insufficient spaces to download or install anything. I don't know what to do because this is the first time I use android and I which someone,anyone could help me on this. THANK YOU ^^

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