Honestly hard to figure out without being able to replicate. I find the time it takes to sort this stuff, for me, could be better spent just finishing the project in the version it was started in. Finding the needle in the haystack just doesn't offer enough reward for me to justify the journey. It's hard enough for developers to ensure smooth transitions with their own components. Trying to ensure every variable covering every third party plug-in is foolproof in transition is wishful thinking at best. If I find myself with so many unfinished projects from previous versions I question my own efficiency and how important those projects were if they have been sitting around a year or more. When I do decide I want to revisit an old project in a new version. I actually prefer to strip the plugs and start from scratch as far as effects. I like to think I have gotten better since I abandoned the old project.

Yes, dubdisciple . . . If I remix them all again in X3, it wouldn't be the worst thing ever, because I think my mixing skills have improved.
 
However, I shouldn't have to,should I? I have 10 or so projects built in X1, and the ONLY reason I upgraded to X3 was to gain the sidechain functionality that VST3 plugins can provide.
 
I waited (obviously) for a few years to upgrade - under the assumption that my old X1 projects would work fine. I was given no reason to feel otherwise. "Just Upgrade!" they said. Others have upgraded - their old projects (apparently) run fine . . . why not mine?
 
 
Anyway, I feel there must be an answer to my situation, I just don't know what my next step is. If the next step is "Reinstall X3 again" then I think I'd be more likely to just rebuild the X1 mixes in X3.
 
I bet someone out there knows something . . .. ?
 
thanks again,
-Tom
 
 

Tom, hope you know I was not dismissing or belittling your concern. I made sure to specify that what I said applied to me and how I approach old projects. The fact that your problem seems isolated makes it hard to quickly answer your questions. Ideally someone with the exact same plugins could open your projct and see if same results applied. If it was me and burning curiosity was getting the best of me, I woukd systemattically save copies of project changing each to remove one plug at a time, hoping to isolate or at least narrow variables down.

Not having most of the plug-ins mentioned I can't comment from experience. If the plug-ins have both VST2 and VST3 formats installed, one thing to try is disabling the VST3 migration settings in Preferences > File > VST Settings. This will prevent old projects from automatically swapping out VST2 plug-ins with their VST3 counterparts. Both formats will be available for future use.

Scook may onto something. Several vst 3 plugs have known issues with Sonar.

Thanks scook, I will try messing with vst3 preferences . . .
 
Dubdisciple, you and I think alike! Logically . . . I started doing some saves in X1 with certain plug-ins removed . . . but I think it's not related to any particular plugin . . . rather, it's the total amount of plugins. 
 
In X1, my project has 50+ tracks and loads of plugins. Can't play them in X3 because the audio engine won't even start/sputter/come to life UNLESS I start deleting the plug-in instances, about 80% of them. It doesn't matter which plug-ins remain, or get deleted. Funny, huh?
 
I suspect I may have  a VST 2 - VST 3 issue. Keep in mind, I can start a fresh project in X3, load in many tracks, and lots of vst2 AND vst 3 plugins, and the audio engine purrs and all works a treat.
 
Is there a list of VST3 plugins that don't work well in X3? That would have been nice to see before I upgraded  :)
 
The plugins in question are Equilibrium, Glue, Soundtoys, S-Gear2, Toneboosters Barricade, and VBC.
 
thanks, guys, I appreciate the feedback!
-Tom

Make sure the plug-ins are up to date. IIRC, DMG recently (maybe a month ago) patched their plug-ins fixing some issues with SONAR.

Scook = Genius.
 
I have tracked it down to Equilibrium Mono, the VST 2 version. Kills any X3 project. Stereo Equilibrium of both VST2 and VST3 works fine.
 
I'm off to download the upgraded DMG Equilibrium . . . MANY THANKS to scook, dub, YouDon'tHave, and John. I'll report out my hopefully good results . . . great forum thanks . . . -Tom

Glad you were able to figure it out.  Sometimes it takes a village.  now if someone could help me figure out JACK on linux. lol

Slackware and I go way back. I even got Ubuntu to work reasonably well with my TV card. That was until it was automatically updated beyond working. That was over two years ago, stopped using Linux then. Still mess with MinGW occasionally but since I don't have a professional need for Unix I just don't have the desire to keep a Linux partition around. In short, I don't know jack.