I had problem with a particular filament that was highly prone to cantilevers that curved upwards during drying. Twice (perhaps three times) the machine collided with the still firmly attached model to detect an error and move the print head to a recovery position.
Once I got and babysat the settings to reduce temperature as the cantilevers grew shorter with the growing object things seemed OK. For a while. I went through the machine (again) tightening all screws to find a number that hold the Z-axis vertical rails in place quite loose. After tightening print quality improved but was still not like when new.
I watched as a particularly wide object printed to see the print head making considerable vertical movement for across the work surface. Then I noticed that the Z-axis was quite skewed with the two vertical screw rods at least three full threads out of sync.
I followed the Z-axis belt replacement instructions–an easy process–to re-level the Z-axis and resume perfect printing. The belt itself [seemed] in very good condition with all ribs present. The belt did though leave a difficult to remove residue on my fingers that I associate with general and normal wear.
I am nearly certain that this problem was not only related to the collisions but also grew progressively worse such that the print head rail was far out of parallel to the print bed.
Lesson learned it seems. If you have a collision that causes the machine to detect the error I believe it best to IMMEDIATELY re-level the Z-axis.