We are using one of the I2C shields for our application (https://store.ncd.io/product/i2c-shield-for-raspberry-pi-3-pi2-with-outward-facing-i2c-port/). We recieved Rev. C of this board. While debugging some I2C issues, I found that the pull-up voltage between the Raspberry Pi and the Shield was 3.6 and 3.7 volts.
Does anyone know why the pull-up voltage is above spec for the Raspberry Pi? Does anyone know a particular Shield that does not have this problem?