There are a couple of factors that can cause the commission rate displayed in the Publisher Hub or Editor Toolbar to not to match the % revenue received.
Gross not Net
The biggest factor is that the commission rate shown on the merchant pages is gross, meaning you see the total rate the merchant provides, before accounting for Skimlinks' rev-share.
The performance pages show net commission revenues, which are 75% of the gross commission. This is the amount that you, the publisher, will receive once confirmed.
Average rate received
In some cases we are unable to pull merchant commission rate data into the publisher hub automatically. Rather than have manual rates which need to be monitored and amended each time a merchant changes the rate, we instead use an average of the rates we have received.
This is meant as a guide rather than an accurate reflection of what you will receive.
Tiered commission rates
The main reason that the average commission rate should only be thought of as a guide is that many merchants offer tiered commission rates. This can be based on specific products, basket size or customer type (new or existing), etc.