New to CodeMix so had to find my way around. The problem was with Python sources. It seems the VS Code associated with my CodeMix (vs
CI 2020.7.22) was 1.40.1. I found that I had to download this version of ms-python vsix, then it works. Even so, the mouseover displays aren’t overly helpful in any case. Anyway, hope this helps anyone having the same problem.