I printed a phone case purely as a test.
So, I was more than happy to try and tear it apart, whilst I am disabled, I should have been able to do something if yours failed like that.
I couldn’t, the layers bonded perfectly even up the thinner side walls that would wrap the edges of a phone.
The filament does recommend drying it before any use, including straight from the supplier.
While I didn’t, did you?
Another question: You said you used the dark grey filament, but they do not have a dark grey; the only grey is rather light. It is far too light for the one yo have in the picture.
Could you also explain…
Did you try to print one part as PLA Matte and another as TPU for AMS hoping they would bond?
TPU is a blanket term to classify a range of stiffness levels as described on the shore scale.
Some people have said this TPU for AMS is around 65D and the more common, but, by no means true TPU is 95A. There are many as you can see from an earlier answer I gave on the subject.