As traders resume crash positions just weeks after the biggest market rout in years, here is Bank of America with a warning of what can really drag stocks lower. Spoiler alert: yes, it's volatility once again, and specifically volatility, which last time was contained to the stock market, "becomes contagious."

From BofA CIO Michael Hartnet:

Market structure concerns continue to grow: short equity volatility AUM ($66bn) + volatility-based & risk parity equity leverage ($200bn) + CTA AUM ($250bn) + risk premium/factor allocation ($300bn; link) = $816bn of “market structure” that could make the recent VIX ETF/ETN implosion a dress rehearsal for a major market correction if volatility becomes contagious next time.

Our equity derivatives team estimates that in the Feb'18 correction, quant funds had to unwind $200bn in 2 days.

This amid a market climate of record bullishness despite February's vol quake.

And as a reminder, here one of the "ABC" warnings highlighted by BofA yesterday which would suggest a market top:

if semiconductor (SMH) & tech stocks (XLK) cannot make new highs in the next week or two, particularly at a time of soaring consumer confidence, then market highs could be seen in for the  next couple of months.

For now, it's not looking good.