When mobs are encased and a piston pushes a block to suffocate them (as in a mob softener), they either go through the wall immediately or they get pulled in with the block when the piston retracts as shown in the attachments below.
The example in wich blazes go through the front is in an actual blaze farm with this design that was working fine in 1.19.41.
It affects 1.19.62 - 1.19.50.
Latest unaffected version: 1.19.41
Multiple