Hello Melissa B.
a) If you set the minimum match value to 100%, even a small formatting difference, a thin space instead of a normal space etc. will prevent autopropagation. Could this be the reason?
b) It depends on the size of your TMs how long it takes for the results to be displayed in the Translation Results window.There is the "LookAhead" option to speed this up, but that can cause problems when you correct a segment you've already confirmed - you might get the pre-correction segment as TM result.
c) The default setting is to display Concordance Search results if there are no TM results. The Concordance Search window looks very similar to the Translation Results window, but you can't copy the results with CTRL+T. Is that a possible explanation?