Upper speaker not working after disassembling

I had to replace the screen on my Moto G 2nd and thus, I disassembled the phone. After putting everything together, the upper speaker does not work any more. I tried a lot of times to readjust the speaker but in most of the cases it did not work at all. Sometimes, I heard something, but the sound had very poor quality with lots of cracking in it. Furthermore, in many attempts I saw that the speaker was attached to the vibration motor magnetically when I opened the case.

With a new screen came a new case, so it is not the original one. Could there be something different? Should I try to glue the speaker on its place such that it is not attached to the vibration motor? Maybe the speaker is too low in the case? It is connected to the mainboard via the rear side. Did anyone have similar problems?

Thanks in advance!