Here is what the Forum knows about Android 8
https://groups.google.com/forum/#!searchin/mitappinventortest/%22android$208%22%7Csort:date
We do not know why your app performs better in Android 7 then in Android 8. You did not post your block code.
Does this difference disappear if you build the apk rather than using Companion? If you do not share your blocks, this might be the best guess that Companion performs differently when used with Companion versus the compiled app. Try compiling and installing on both devices.
Regards,
Steve