Kavanaugh is the only one who hasn稚 written anything from the April sitting.
So? Its not like its a rule that they should be spaced out among justices. Plus there are plenty of other big cases remaining that he could get over an April one; I think he might get the EPA case if they don't want to let Gorsuch end Chevron deference. Plus, even if they did want to give him something from April, Biden v. Texas is still available too.
If Biden wins
Biden v Texas, I imagine the opinion is a per curiam dismissal of Texas' lawsuit. That would make the opinions for the April sitting even.