I'm unable to right click a clip and show the menu normally when I do the following in 19.04 in Windows.
Add a file to the project bin > drag the file to the timeline > seek anywhere in the clip > right click the clip
The menu shows for a split second and disappears. I have to hold down the right click button for the menu to continue to show. If it has audio it says "Set audio reference before attempting to align" in the status bar. This makes it awkward when using a touchpad. It this normal or a bug?

Yes, this is a known bug: https://invent.kde.org/kde/kdenlive/issues/132. Workaround: as you descript: keep hold down the right click button for the menu selection.