Powering multiple pistons simultaneously create frame rate drops compared to previous versions (i.e 1.15-1.15.2) regardless of the type of hardware the client is running on to the point of freezing the game in lower spec hardware. Multiple pistons like piston walls or large and complicated piston and slimeblock contraptions.

Video proof:

https://youtu.be/rItF9CHJZ4w

Video not mine.