Storage used after flashing on violet

[D.L.Tejas]

I have Pixel Experience[9.0] on my Redmi Note 7 pro currently,it runs perfectly,but this one issue I observed is occuring across many roms and that is the system uses 10/10+GB of internal storage after I flashed any custom ROM even lineage and Resurrection Remix and now Havoc too!!!......I tried to find if any log files resided in root directory>data/log using root but there's nothing and still it shows 18% storage used!!!!!.....why?
My phone has 64GB internal storage
Can anyone help me fix this....Please