I created a guitar track with template. Recorded track lanes and selected the best recordings using comping. When I now want to add an effect to the track, it is greyed out. Other tracks in the project work ok, same vst on new tracks also works well. 
 
Of course I can copy my clips (got several with this problem) to a new audio track. But this wasn't the reason for me to use track templates. Or could it be something else?
 
Frank

Right-click in the FX rack to see if the rack is bypassed.

Easy as you say, tx! Any idea how the full fx-rack got bypassed?

It happens automatically when a track is frozen with the "Track FX" freeze option enabled.
It happens manually with keyboard shortcut "E" or the FX button in the Mix Module.