Hiya there!
For each payout on the payout page, there should be a link to view more details around it; 'Payout Details'.
There you'll see all the different adjustments that go into the payout amount before it's sent to you. Such as tax, itch'io's cut, payment processor fees, and then a bunch of additional things that could potentially be affecting things, such as chargebacks, refunds and the additional payout fee.
Hopefully that'll help to get to the bottom of things regarding any potential deductions!