When I import a certain sequence of RAW files into Lightroom from LRTimelapse, I go and begin to edit the keyframes as I always do.  However, with this sequence, I seem to be missing the masks that are created by LRTimelapse.  In the develop module, when I select M or Shift M, there are no masks.  What could be the cause of this?  Anything I could check?  They appear for all of my other sequences.  Also, "Show Edit Pins" is set to "Always" in Lightroom.

Try to reinitialize the sequence in LRTimelapse (metadata/initialize). Then go through the first row.
In Lightroom go to grid view, set filter "LRT Full Sequence" then "Metadata/Read Metadata from files".