Tempo Track Going Haywire in Cubase 11

Has anyone ever seen this before? When I place a point on the tempo edit line, the project immediately jumps to the right, so the point appears nowhere close to the chosen location. (I’ve placed entries on the Arranger Track to make the shift obvious.)

When I try to place a point next to it, the point does appear there (though of course that’s not where I want the edit). But then, when I try to place and move an edit point between the two, the project shakes from side to side (often violently), and the edit point suddenly moves sideways at random. (The three back-to-back videos contained in the attachment show this.) This happens with both ramp and step editing.

I am hoping that someone might provide some insight into this issue!

Thank you.

Cubase 11
All drives are SSD