Slime piston flying systems do not work properly

Summary:

I was making a flying piston system with a slime block, in order to break a plantation, but I noticed that the system didn't work as needed, in fact, it broke 100% of the time, always in the exact same location, no matter how many times. would be redone

Steps to Reproduce:

I'm putting a video below, showing how to do the system

Required items: 4 observers, 2 pistons, 2 pistons with slime, 14 slime blocks

Observed Results:

Many times, the piston ticks did not work at the right times, which caused the machine to go back and forth immediately, or sometimes, go only part of the way and come back all over again. 

I also noticed that there were times when the slime block did not hold the pistons with it, abandoning them halfway and breaking the system.

Expected Results:

The pistons should work according to their ticks, correctly, not blocking the entire system

The slime blocks should keep the pistons stuck to them, not abandoning them midway