Due to changes to falling block physics in 1.18.2, presumbably connected to MC-248858 they sometimes start behaving a bit erratically. For instance - it's possible for 2 falling block entities to fall on the single spot, which makes it possible only one of them to convert ot to the block, when the other drops as an item. That in general makes it rarely drop cubic gravel blocks when you use a shovel with Fortune 3, which has never been before (it has always been dropping flints only) and probably must not happen (similar to manner Slik Touch shovel used on gravel always drop cubic blocks and not a single flint).
How to reproduce:
Go to Nether 15 height, give yourself pickaxe eff 5, shovel eff 5 AND fortune 3. Find a gravel vein and dig it out from the bottom. Notice it will drop some of cubic gravel blocks, which has never been before.
I believe this issue is the same as MC-207133. What's happening here is that the gravel is stacking inside one another whilst it's falling and it's able to do this because when any block is falling, it is considered an entity. When the stacked gravel eventually reaches the ground, it turns into its block state and as you may already know, multiple blocks cannot occupy one space, therefore some pieces of gravel drop as items.