[SOLVED?] Speed Comping Not Working

This issue was not actually solved for me (I just worked around it and moved on) but I'm marking the headline [Solved?] because there are some good and potentially useful answers here for anyone who runs into these difficulties in the future. Thanks, everyone!
I do this so rarely these days that I almost always have to watch a video tutorial to get started, so I was pretty sure I was doing it right. Here's my story:

• I have five complete vocal tracks, recorded in "comp" mode.
• I open the take lanes and use the smart tool in the bottom half of a lane to create "logical" split points throughout the song.
• I set up dim solo and solo the vocal track. Now I can hear the band, but "dimly."
• I press shift+spacebar to start playback for comping. Playback loops within the first split section.
• I can move playback to the next section, and the next, etc., using left and right arrows.
• Up and down arrows move to the various lanes.
• But I can't hear any of the takes except for the most recently recorded one, which is on top.

When I look at the waveform, it appears to be kind of a "ghost" waveform. If I click on any one of the sections, it does not get promoted. All takes are silent except for the most recent one. I haven't been able to get any of the earlier takes to play, much less to participate in the comping.
Anybody know what could be wrong?

Verify that ALL the takes have neither Solo nor Mute buttons active.  I was able to duplicate your situation if the most recent take was in Solo mode:  None of the other takes could be heard, even though the Speed Comping function appeared to be working.  If this isn't it, send me a screen shot of what yours looks like and I'll give it a look.  I used Speed Comping every day until recently.  :)

OK, I went back and messed with the region mute tool. You don't use it above the timeline, and you don't use it on the bottom of an individual track (or lane), and don't expect it to work on multiple tracks (or lanes), either. It works if you swipe it on the top half of a track (or lane) and if somehow you've accidentally muted a stack of lanes, you get to unmute them with this tool one lane at a time.
 
So I did this, and I could see the waveforms normally and hear the takes. Then I tried to comp the vocal again. This time all was well, until it wasn't, which happened at a different place near the end of the timeline, at which point I was hearing all the takes at once. (Also, randomly during comping the backing tracks were muted for a few bars, although luckily not erased.)
 
I deleted the end of the vocal and sang it again, punching in in overwrite mode where necessary. Maybe I've had too much coffee. Something in SONAR is screwed up, and this forum has always been a great place to get help, thank you all, but with the developers all gone it just seems pointless to spend a lot of time figuring this out. I've got what I need right now, so I guess I'll count my blessings and mix it down before something else goes south.
 

If worse comes to worst, another option is to shift drag the entire takes into individual tracks. Not as convenient, but you can comp using tracks (and should be immune to the odd behavior you are seeing).