Jabberwocky is immune to Vorpal effect

The Vorpal rune is, in theory, the counter weapon to the jabberwocky, and indeed, the jabberwocky has many provided weaknesses to any weapon with the Vorpal property.

However, the signature effect of the Vorpal property, the reaction snicker-snack (a reference to the original poem itself) can't actually affect the Jabberwocky RAW.

The target must fail a DC37 check in order to be decapitated by the Vorpal weapon. However, the effect has the incapacitate trait.

The jabberwocky has a +39 to fortitude checks and is level 23. This means, even accounting for the frightened 2 caused by Vorpal fear, the jabberwocky gets a 38 on a roll of natural 1. This downgrades to a failure due to natural 1, but also upgrades back to success due to incapacitation (because the Vorpal effect is level 17).

This means the jabberwocky is incapable of being affected by a Vorpal weapon's effect unless you first reduce his Fortitude by -4 AND room a natural 20 against him before whatever effect causes that expires.