When breaking a slime block while it is being moved by a piston there is the possibility of the particles (visually) being lava particles.

I'm unsure about the timing, but as shown in the below video, it can happen and does require a few attempts.

This is similar to the other tickets relating to "wrong particles with block moving" however this block does not display the piston "head" particles.

https://www.youtube.com/watch?v=DQTN31hCFiA