Always 255-response in I2C between ATTiny85 (8MHz) and Arduino Uno
It may seem that the current commit of January 2018 from the TinyWire library is corrupt. Try using an older version from 2017, for example this one: https://github.com/rambo/TinyWire/tr...72a13504bbfc4e

This solves the problem for me as well.

Source: Teensy 3.5 - I2C - ATTiny85-20PU (TinyWireS.OnRequest not triggering!) - Post #11