[thanatropism]

Well,

1) To track the actual index, index funds must continually rebalance their portfolio. In a liquidity pause they may not be able to do this, thereby becoming a non-index fund. Actively managed funds have the portfolio they have -- unless they're defrauding the public somehow. An index fund that becomes a non-index fund would fall in this latter category.

2) The index (not the funds) is assumed to reflect all the information that can be used to make some money by arbitrage. This process is referred as "price discovery". But in a liquidity pause, price discovery grinds to a halt. Actively managed funds have their own idea of what are the fundamental prices beyond what the public leaderboard says; their price discovery is not beholden to the existence of a liquidity market. Actually -- if the market goes for years with very low liquidity, it becomes more likely that people who, say, are shorting Herbalife for fundamental reasons, have more knowledge than the index. In this way the index is like an AI that can become starved for data.