When using CMD+click to squash 2 commits, it seems to be showing the wrong commit after you CMD+click the second commit.
e.g. you have commits A - B - C (from top to bottom), if you select A, then CMD+click C, B is shown in the preview pane on the right (I would expect either A or C to be shown, since those are the 2 I’m working on).
Right clicking C and choosing “Squash Selected Commits, ignoring new messages (fixup)” does correctly merge A and C (and properly discards the commit message from A).