I have just tested with build 1916 and it's now working as specified, but I feel that HWiNFO should display all the values on startup even when the GPU is offline and then zeros when it refreshes.
The clock speeds reflect the P-State the GPU was in before it went offline. If the GPU in in P-State 8 when I start HWiNFO then these clocks are shown as min/max/avg when it's goes offline. If it's offline and I start it then initially it's on P-State 0 and these values are shown.
I also found if I press [Reset Values] when the GPU is offline I get minimums of zero wihich is not ideal. I have just changed SIV to set both the average and maximun to be the minimum rather than set all three to zero.