I can correctly read the device ID from the HDC2021 with the MSB returned as 0x07 and the LSB returned as 0x0D, as well as the manufacture id as 0x5449
But the MSB of the temperature (address 0x01 returns a constant which varies. The LSB read returns data than moves and rolls over with temperature as expected.
A read of register x04 prior to reading the temperature returns data = 0x80 => data is ready.
I sent a soft reset to the device (addr 0x0E = 80) and and I got the same results.
The timing minimums exceed twice those in the data sheet. Clock speed is 189Khz.
The humidity sensor is returning reasonable data which varies with temperature changes which are likely changing the humidity, so I suspect it is operating.