I posted an edit to the top comment in hopes that it will get changed for anyone looking at this post in the future but in case it gets rejected here is the actual issue and fix.

If you just want the solution skip down to the bolded text.

I came across this post while browsing for resources to document my own experiences with "filament slip" in Makerbots and every suggested solution was wrong and potentially malicious to the machine. I'm an expert in the field and have taken apart and fixed dozens of machines.

First a bit about the anatomy of the extruder so you can understand better. The way that the toolhead detects slips is with an encoder wheel placed above the actual drive mechanism, not attached to it or the idler whatsoever. It's also not even tensioned against the filament at all. The filament is "held" in place with an injection molded piece of plastic that attaches to the rest of the extruder body just by the pin connectors on the internal PCB and a small positioning groove on both sides of the case.

The encoder wheel and its sensor are very unlikely to wear but what happens to every older head is that either the casing or the injection molded part that holds the filament wears and the encoder wheel no longer presses firmly against the filament which causes the filament to move without turning the encoder. The encoder then not moving while the drive gear is, reads a filament slip and sends an error message even though nothing is mechanically or functionally wrong. The wear is also not clearly visible even on close inspection. This problem seems to arise in every Smart Extruder+ once it reaches 150-200 printing hours.

Actual Fix As a temporary fix you can jam a piece of foam inside the right side of the extruder to push the poorly secured injection molded part against the encoder wheel. This will make the filament slip error much less frequent but won't completely solve the issue. I'm working on a 3D printed insert that should hold the part more securely, at least until the printed part wears after an additional 100 or so printing hours. I'm also working on a 3D printed replacement for the extruder body and some of the injection molded interior parts. It aims to be a drop in replacement which should greatly improve both reliability and functionality. If I can remember once I'm finished I'll come back and post a link here.

I posted an edit to the top answer in hopes that it will get changed for anyone looking at this post in the future but in case it gets rejected here is the actual issue and fix.

If you just want the solution skip down to the bolded text.

I came across this post while browsing for resources to document my own experiences with "filament slip" in Makerbots and every suggested solution was wrong and potentially malicious to the machine. I'm an expert in the field and have taken apart and fixed dozens of machines.

First a bit about the anatomy of the extruder so you can understand better. The way that the toolhead detects slips is with an encoder wheel placed above the actual drive mechanism, not attached to it or the idler whatsoever. It's also not even tensioned against the filament at all. The filament is "held" in place with an injection molded piece of plastic that attaches to the rest of the extruder body just by the pin connectors on the internal PCB and a small positioning groove on both sides of the case.

The encoder wheel and its sensor are very unlikely to wear but what happens to every older head is that either the casing or the injection molded part that holds the filament wears and the encoder wheel no longer presses firmly against the filament which causes the filament to move without turning the encoder. The encoder then not moving while the drive gear is, reads a filament slip and sends an error message even though nothing is mechanically or functionally wrong. The wear is also not clearly visible even on close inspection. This problem seems to arise in every Smart Extruder+ once it reaches 150-200 printing hours.

Actual Fix As a temporary fix you can jam a piece of foam inside the right side of the extruder to push the poorly secured injection molded part against the encoder wheel. This will make the filament slip error much less frequent but won't completely solve the issue. I'm working on a 3D printed insert that should hold the part more securely, at least until the printed part wears after an additional 100 or so printing hours. I'm also working on a 3D printed replacement for the extruder body and some of the injection molded interior parts. It aims to be a drop in replacement which should greatly improve both reliability and functionality. If I can remember once I'm finished I'll come back and post a link here.