I would like to report something extremely annoying which happened to us a few days ago.
We had a Matomo v3.3.x (I think) that we had just migrated from an old server with php 5.6. On php 7 it worked fine. So, we decided to upgrade it. The upgrade message was indicating an upgrade to v 3.4.x. But the process turned out to be very long, and I got very surprised when I saw that it required a database upgrade. After the process, we saw that we had now Matomo 4 !
In my opinion, it is a major problem to have a false information before making an upgrade. you don’t take the same precautions when you make a minor or a major upgrade.