Stablecoin bug?

hi guys - I note on my dashboard that I seem to have made a stonking return on my USDC stablecoin. I’m honestly scratching my head trying to figure that out, as it means a massive ramp up in taxable gains.
I’ve attached where I think where the issue might be in terms of calculation re: unit cost vs market value?
Any thoughts - am I missing something??
Effectively I thought stablecoins are essentially a peg, with no prospect of ROI???!. Grateful for your thought!

Screenshot 2020-09-27 at 12.58.43 PM|318x116

Are you missing purchase history for some portion of those coins? I had a similar situation where some of my coins did not have purchase history and the “gain” was therefore 100% of their value.