What is happening to Horizons S&P 500 index fund?

[vb73]

Hi, first post. I'm freaking out right now because in the last month, Horizons ETF HXS.TO has become completely untethered from the S&P 500 it purports to track.

So i compared it to the comparable Blackrock fund, Ishares XSP, and if you look at the chart I link to below, you can see that XSP tracks the S&P 500 much more closely than the Horizons fund. Historically the Horizons fund has outperformed the S&P 500 (which is a red flag because it's not supposed to do that), and now it's begun underperforming the S&P 500 in the last month. (see the second chart I link to below)

I don't believe this is part of the "index fund/etf bubble" some have warned about, because it seems unique to this particular etf. Can anyone more experienced than me weigh in on this? Obviously I have a substantial holding of it, so I am concerned the direction this is going in.

[Historical outperform]https://finance.yahoo.com/chart/HXS...lQ29sb3IiOiIjNDVlM2ZmIiwicmFuZ2UiOiJtYXgifQ==

[Underperform this month]https://finance.yahoo.com/chart/HXS...lQ29sb3IiOiIjNDVlM2ZmIiwicmFuZ2UiOiIxbW8ifQ==