A lot of our push back comes from legal. There are so many boxes to check during the removal process it becomes a year long ordeal.
“Pushback from legal” usually means documentation and rationale weaknesses. Which is largely due to the MSPB being very employee friendly.
The servicing HR and attorneys should be offering training before these issues get out of hand.
From my experience, (and I don't know how unique our command is) the issue can be boiled down to the fact that we change first line supervisors every 2-3 years. We have a brigade of civilians working different jobs under the same PD in a 24/7 environment. Who a civilian reports to and their rating chain changes all the time.
The documentation becomes a problem because it has to start with a first line supervisor. Verbal, written, and then a 6 month PIP, which easily becomes a year long PIP is any improvement was shown.
First line supervisors aren't given access to an employee's file unless they go seeking it, which most supervisors don't do unless they have a reason to. This makes existing issues seem "new" to a new supervisor unless they were aware of the behavior before.
We've also had an issue with employees complaining to legal when one supervisor will write them up for something a previous supervisor didn't. This gets thrown into middle management's face about consistency and often derails the whole process.