As of this post, I have come to know of one known MetaStock issue for which, in rare cases, the very useful CUE Global Commentaries may not display.
The issue was not related to CUE Global. For the one user who reported this, the Commentary did not appear for other, non-CUE, expert advisors too.
Upon contacting MetaStock support, it was found to be a known issue.
Depending on whether the Commentary window is docked to the top or bottom or floating, sometimes (in very rare cases) the Commentary may not display.
Apparently, docking it to the left or right it works under those circumstances - as a workaround.
MetaStock is aware of it and may fix the issue in subsequent releases. For the meantime, one may use the workaround mentioned above.