APs are not paid a fee by the fund. They participate because creation-redemption gives them a profitable arbitrage whenever the ETF drifts from nav. That incentive structure works well in normal conditions and is voluntary in stressed ones: nothing compels an AP to keep arbitraging a fund whose underlying market has stopped pricing.
Funds with several active APs generally hold tighter to NAV than funds with one. The number of APs is disclosed in the annual report and is worth checking for niche or illiquid ETFs.
Example: a bond ETF's underlying market freezes. Two of the fund's three APs step back, and the ETF trades to a 6.2% discount to a stale NAV for several sessions until normal quoting resumes.
Related: creation-redemption, etf, nav, premium-discount-to-nav, market-maker