When an item or entity goes into lava there are too many splashes. Instead of just one it makes one for everyone time its colliding with the lava.
Im using Fabric Loader 0.12.12 with the latest update for fabric API
For ex:

Note i did test it without item physics and there was no difference

up

Also I tested it on the fabric loader 0.12.11 and this was not an issue, it only happens on 0.12.12

If you would like me to give my mod list I can

Related: when Striders walk on the surface of lava, they cause continuous splashes every frame

Very much the same here + lava splashes appear continuously and not even in lava, when you are on egde to lava and start to jump it splashes a lot.. like tripple times.