This is the second time this has happened.  Can't figure it out so I'm hoping someone here can shed some light.
 
I've multitracked drums, and have created a composite take from about six take lanes.  Everything sounds fine, but after working on the track for a couple of weeks, the track for the last floor tom (there are four tom tracks) sounds doubled, or as if I was playing a flam each time it's struck. This particular track is panned almost hard right, and the tom is also audible from the other tom mics a bit, as well as the overheads. But what is weird is the "doubling" or "flam" effect, which appears to be positioned in the center.
 
The only way I can eliminate the doubling is by soloing the track.

Hi. It sounds like a routing issue (send, aux track, patchpoint). Or could it be a phase issue, introduced by some heavy eq settings? 
Best of luck.

I had exactly the same issue on my last mix of drums too which was 14tracks from drums only.
I thought i must have accidentally moved a track, no.
I ended up having to close sonar and reopen to fix.
I haven't tried any mixes since latest update and hadn't ever had problems before the last update either.
Not much help, i know!

I was thinking phase issue also. You don't have Channel Tools in the FX bin, do you? Sometimes it can introduce some nasty artifacts.

"The only way I can eliminate the doubling is by soloing the track."
 
So what other tracks are picking up this tom?
 
If you mute this tom track and it's still audible in 2 or more other tracks, do you hear doubling on those?
 
If you don't then  it sounds like the track might have been nudged by a few ticks in the timeline - classic case of phasing issues, as already suggested.
 
 

Bristol_Jonesey
If you mute this tom track and it's still audible in 2 or more other tracks, do you hear doubling on those?

Yes, a little bit.  Good idea though; I hadn't thought of trying that.  Pretty sure I never moved/nudged the track, but anything is possible. 
 
Nothing in the effects bin.  It really sounds like it's a phase thing, but nothing I tried worked.  Really bizarre.
 
I had to revert to an archived version of the project. Nothing I tried worked.
 
I just installed the latest upgrade patch.  Hopefully that prevents it from happening again, but I'll be saving versions of mixed projects from now on until I can really determine what the hell happened here.  On the other tune that this happened I don't have an archive I can use so I have to re-record those drums.

You would not happen to have offset (mode) engaged on one or more of the tracks, making it play double?

I don't even know what "offset mode" is.  How would I check if it's engaged?

You could check in the Inspector (I), or on the control bar. Do not know if it is your problem or not, but could be worth to check.

All the best.
 

Thanks, but that wasn't it either.