Hello,
(I am posting this for future reference in case someone else hits on the same problem).
I am building an LAB diagram consisting of Logical Components and Component Exchanges.
After a sequence of edits, the labels on the Component Exchanges became invisible.
I tried the following to make them re-appear:
- Pressing F2 on a CE brings up the label for editing. After editing it is invisible: no success
- Label Color is non-white (so it does not blend into the background): no success
- I set the filters to default, so Hide Component Exchange Names is unchecked: no success
- I did a Show/Hide cycle on all elements: no success
- Refresh diagram: SUCCESS!
Frankly this is the first time I tried refreshing the diagram. I am very pleased it worked 
And now, back to diagramming. I hope it is obvious that I do not need help at this point.