Hi GT3RS, Welcome to the forum!

You didn't mention if you had tried fishing. That CC are feeding but HBG are not could indicate issues but not necessarily your deepest concern (major kill). You did not mention the size of the HBG when you stocked. If they were adult sized (~6") they may have already been 2 years of age or more. The LMB would clean out limited reproduction and if they were 2 years of age when stocked then they are entering their 5th year. There is some mortality every year but this picks up as HBG get older. It could be that this natural mortality has opened space for pond organisms to flourish providing the surviving HBG with lots to eat. Where you don't get recruitment you may need to overstock 6" HBG every 2 years or so. So maybe at 1/2 the rate of you originally stocked.

A dead fish doesn't always float. Maybe more often they don't when dying over winter. But at this point you should try to determine survival by some method other than feeding. LMB should strike an inline spinner and so should any surviving HBG. Either way, with a strong population of LMB you will need to overstock the HBG.

I am hoping all you need is a few more HBG. Try to do some fishing an let us know.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers