My understanding is that nothing serious has gone wrong, so far, in nearly two years.
GBTC is a bad way to trade bitcoin and the chart in reference [2] you posted shows exactly why. A good BTC tracking ETF would have NAV = market cap, but here you can see that NAV and market cap are unlinked (as are returns for GBTC vs bitcoin) and people are generally paying way over NAV (in some cases over 50%!) to own GBTC. This is presumably due to unsophisticated traders buying GBTC without understanding that they're getting a terrible deal.
In summary, yes something is seriously wrong with GBTC and has been wrong for the entire life of the product.