Derooie Clear story. Please note that if you turn off ZeroFX, you will be charged extra rate storage, so in the end you will be a few percent more expensive.
Those 1st transactions you now get are based on estimates, which are corrected to the actual exchange rate with the 2nd and 3rd transactions. These amounts are therefore close to each other.
With ZeroFX off, however, your 1st (and only) transaction is skimmed up to make sure bunq never loses on it, so you actually get an unfavorable rate.