C14 Pro W10
I have a very small project with a few VSTi’s (including PianoTeq 8), and a few audio tracks, with many lanes/takes associated with the latter.
Everything was fine until I added two extra beats in a measure. Some time after that I realized that the recorded piano MIDI in the PianoTeq VSTi MIDI track editor was out of tune with the piano synth itself - the PianoTeq MIDI was high by 100+/- 40 cents or so compared to the piano synth (embarassing, but I’m not 100% sure now, a few days later, whether it was just sharp or just flat of being 100 cents too high - I’d lean towards just sharp). The way I tested this was to compare what I heard when I hit a piano note on my synth, vs. hitting the corresponding note on the piano roll keyboard in the PianoTeq VSTi MIDI track editor.
I thought that somehow I clicked some wrong thing while inserting the extra beats. To trouble shoot, the first thing I did was to see if my synth transpose button had somehow been inadvertently pressed, or if any of the Cubase transpose functions I knew about had been activated - none had.
I am an over-the-top-project-saver, so I went back to the project just prior to the one where I added the extra few beats, and I was shocked to find there was still the same discrepancy between my synth keyboard sound and the notes on the keyboard of the MIDI editor in that earlier project (the latter being higher).
I shut down the keyboard, saved the latest Cubase project, CTRL-Q’d Cubase, toggled off my interface off/on, turned on the synth, restarted Cubase, opened the project, and the problem was still there.
I repeated the above sequence, but rebooting the computer also, and the problem was still there.
More weirdness - I kept going further back in my projects, and I found the discrepancy was present even on very early projects. I said, "let’s go to the projects at the beginning of the song folder ", (20-30 Cubase projects back from when I inserted two extra beats), and thank goodness I found the synth and the VSTi MIDI keyboard were in pitch with each other in those earliest projects. I totally did not expect to have to do that.
Then this is the weirdest part: Without my making any changes to any projects, I started working my way through more recent projects from those very early projects, to identify the first project where the synth and VSTi MIDI keyboard became shifted in pitch relative to each other. In doing so - I found that projects that had just recently been heard to be out of pitch compared to the synth now were in pitch!
And this extended all the way to the most current project - it had (magically?) gone back to being in pitch with the keyboard synth.
So it’s all good now, everything is in tune with everything else, but I’m wondering what in the world happened there.
I don’t take psychedelics 
. I’m attributing this to Gremlins. But I’m open to any other thoughts, please