What Is the Primary Risk for Liquidity Providers in a Perpetual Futures AMM?

The primary risk is unhedged exposure to the contract's price movement and the resulting impermanent loss. If the pool becomes significantly imbalanced (e.g. too many long positions), the LPs effectively take the other side of the trade.

If the market moves against that side, the LPs suffer losses greater than simply holding the underlying assets. There is also the risk of protocol smart contract failure.