When I first purchased Platinum in January, I discovered that Mix Recall was not only non-functioning in my system it also caused serious crashes and unrecoverable loss of functionality.  In all honestly, it scared me to death. I reported this and some of these problems were acknowledged and were supposed to be fixed in the February release.
 
I have installed the new release and Mix Recall is just as broken as it ever was.  To be honest, I don't see any real use for this feature in my own work flow anyway but I'd still be interested to know if other are having the same problems.
 
If I try to save a new mix scene (say, for example, one without vocals) it takes at least 60 second or so for the process to complete.  Then, if I revert back to the original mix scene with vocals it takes another 60 or so seconds, BUT....
 
At least half of the tracks no longer sound.  Drums are gone, bass is gone, but horns remain and some pianos.  The meters still seem to function but no sound on random tracks.  If I shut down (without saving, of course) and re open the project, everything is back to normal.  I shudder to think what state I would be in if I actually had saved the project.
 
This is identical to the functionality of Mix Recall before the recent monthly release.  I'm perfectly happy with all else in SONAR Platinum as well as the content of the latest release.  But I will not going anywhere near Mix Recall until I have much more confidence in the feature.

Did you change buses or routings? Mix Recall doesn't handle those kind of changes yet.

No, I didn't.  All I did was mute a lead vocal and save that as a mix.  Then I went back to the original mix with the vocal and my project was in a very bad state.  That is to say, several random tracks no longer sounded.  They are not muted.  The meters still function but the sound is just plane gone.  If I Close the project without saving and then reopen it again and everything is back to normal.

Are you using Concrete limiter in that project by any chance, or PC-2A? 
Also if you save the project as a new file after that and reload it does it sound ok then?

Yes, I am using the concrete limiter on three tracks: Session Horns, Drums and Bass, but not on the master buss.  I have the Waves L3-LL multi-maximizer on the master buss.  There are 10 tracks in total.
 
I made a copy of the project and experimented with that. I used mix recall the same way as I have described above (two mix scenes, one with vocal track muted and one without vocal mute).   Switching between scenes I was able to get the failure. That is, some tracks go silent even though they are do not show as muted.  Also, the scene switch took quite a few seconds, as it usually does.
 
I saved the project, closed it, then re-opened it again.  The tracks that previously did not sound are now sounding again.  That's a good sign.

This is definitely related to a known bug with Concrete limiter which we are due to release.
Mix recall itself is very solid and has undergone months of testing. However if you are using effects or synth recall any bugs in the plugins affected sometimes rear their heads. I will send you a test build of CL to verify that it addresses the issue you are seeing.
 
Regarding the time to recall the time is directly proportional to the data being recalled in fx and synths. If you are choosing to recall fx or synth settings it could take awhile. e.g. in the case of Kontakt it could be gigabytes depending on the samples. If you want it to be fast I don't recommend doing recall of fx or synths unless you really are changing patches in the scenes. Either that or save different scenes for the ones with patches. If fx are disabled in the mix recall preferences then it will only take a few seconds to recall.
 

Thanks Noel for nailing the source of this problem so fast.  Sorry for being so quick to jump on Mix Recall when the problem was actually located in another component.  Oh well, how could I know?  Anyway, a bug swatted is a bug dead wherever it happens to live and we are richer for it.  Cheers...

No worries :) When testing the feature every problem known to man was being attributed to mix recall since it unearthed a ton of ancient problems within SONAR and plugins. A large amount of the stability of Platinum can be attributed to fixing these as part of testing Mix recall.