Thanks for this post.
I had the same vibration issue with my new MP40 wQD after I poured in some Calc near the pump. About 24 hours later the Motor just jumped off the tank when the impeller seized. I pulled it apart for the first time and soaked it in citric acid and cleaned it up until it looked new. I then put it back on and it just had a nagging vibration that it did not have before. Then I searched and found this post and the picture you posted just jumped out at me. My white Ceramic rod was stuck in the impeller and I just assumed that was normal and that it spun on the metal shaft;Meh I did not realize there was another inner black ceramic bearing.
Both pumps that I had before were the older MP40s so I was not familiar with the assembly of wQD wetside.
I had to actually tap the Ceramic Rod out as it was welded in with precipitation.
After another quick soak I got out all the white gunk on both the shaft and bearing and now the pump works like new again. Thanks
@redfishreef96 for the picture.