The datasheet, figure 17 (page 27) for the I2C serial port read pattern has a REPEATED_START between the write of the register number and the read of the contents.
THIS IS WRONG. It needs a STOP. Lost a day+ of my life to that....
Also, a minor complaint about that datasheet. It uses the term "Sub Address" but does not define what that means. In reality, it is the register number. Why not just call it "Register number" or register address" or "register index"?