I've seen this happen once or twice with a single block to an Underwater Ruined Portal in 1.17, but this seems to happen more commonly in 1.18, so it is worth reporting at this point. Sometimes (And it seems to be seed specific, meaning it happens with specific Ruined Portals on specific seeds) when a Ruined Portal generates underwater, some of it's lava blocks on an 'ocean floor level' are not replaced with magma blocks. As a result, lava blocks exist underwater as long as the blocks around them are not updated.

This can be shown on Seed 1252312813 at coordinates -923, 62, 2 as an extreme example, and here is additional video evidence as proof: https://mega.nz/file/YMYzXAoT#uaNFjh0Vn02MBOH7krgfpXr9sB6GKitQ3Z8qlO-EGO0 . I have reloaded this seed from scratch and teleported to the same coordinates several times to find the same end result. Hopefully the seed contribution with the issue can help fix the issue at hand.

Steps to Reproduce:

1. Create a new world, using 1252312813 as the world seed.
2. Go to or teleport to coordinates -923 62 2

Observed Results:

Alot of the lava blocks on the 'ocean floor level' created by the ruined portal underwater did not convert to magma blocks.

Expected Results:

All lava blocks generated underwater upon generation of the ruined portal on the 'ocean floor level' should have converted into magma blocks instead of lava blocks.