Any world in Minecraft 1.18 (Upgraded or Generated), any cave that generates below Y=-55, will become Lava Logged. Because of this, any custom worlds with custom heights that go below Y=-55 will have caves that are lava logged. In the images below it shows many examples of the caves becoming lava logged at the y level -55.
Environment
Windows 10, Minecraft 1.18 RC-1, Java 17.01
This appears to be a duplicate of MC-237017.