This glitch has happened ever since 1.8.2 as far as I remember, and it causes non updated lava that generates in layers along with gravel. This world generation glitch usually happens in very small areas, and it can happen at various levels near gravel in the Nether (and not just near the lava ocean like in the following example). This doesn't happen in soul sand valleys or basalt deltas. To reproduce, use the seed 7912444071293930782 and run the following command:

/execute in minecraft:the_nether run tp @p -64 32 -62