Bug contents:

Whilst mining into some Magma Blocks in a ruined bastion as one does in their spare time, I suddenly began to float, similar to levitation effect, but I had no afflictions. I could jump, which would make me hit the floor instantaneously, jump, land, and float back up.

Replication:

With some short testing I found this happens when one has space to jump, is standing on Magma Blocks, adjacent to lava, but not in it. It's more noticeable when crouched. If you need more detail, it happened to me at 381 34 -186 in the nether on the seed 1872986568.