Hi YuKon,
How did you close the app? go back to design mode from running mode?
I tried to open an existing app, when opening it, the memory usage of PowerApps would rise. If I exists the app, the memory would be released slowly.
If I start to design a new app and connect to an OneDrive Excel file, the memory of PowerApps would rise regradless of Design mode or Run(preview) mode. Going back to Design mode will not release the memory.
Maybe you can try to close PowerApps Studio, it will release all memory usage of PowerApps. Then test again.
Thanks,
Wendy