CbB / Splat audio export issues

Brief: I've got CbB projects that sound great on playback but cannot be exported without audio issues. I can only get the project to export correctly by opening it in Splat, and even then it's trial and error with export settings to get a correct export.
 
Long:
 
I'm finding some serious problems when exporting project mixes in CbB. One surf rock style project that I'm working on has tracks sending to reverb busses. Standard procedure, nothing fancy, just a send to a bus that has Altiverb on it, which then continues on to the Master bus.
 
Everything sounds fantastic when the project is played, but upon export, reverb tails are being strikingly cut off like nothing I've ever heard before. hard to even describe but it's like the reverb busses just drop about a half second into the tail. No amount of fiddling with it in CbB makes any difference. My usual export settings are entire mix and everything checked except audible bounce and live input. Tried exporting just the master bus, exporting from the hardware output, no difference. I select all, select the time to export on the ruler, all standard stuff.
 
I've got another project where I've done a simple clip gain automation to roll off the ring from a single snare hit. Again, it sounds great when played but that clip gain automation is completely missing in the export. It's a very obvious snare ringing out during a rest. The ring is gone on playback but still exists in the export, like the automation was never there.
 
In both cases, the only way I've been able to get a correct export is to open the project in Splat and export from there. Even then it's a trial and error process. Regular export entire mix won't do it in Splat either but usually I can get it to work by exporting either the master bus or the hardware output. I've even been able to export from Splat using master bus, save and reopen project, try to export master again and it doesn't work, same issues as above. I'll then try from the hardware output and usually that will do the trick, even though hardware output didn't work last time.
 
I'm baffled. I don't know if it's just these projects having issues or if there are other things not being exported in other projects and I just haven't noticed yet.
I've tried making sure there are no automation nodes past the "end" of the project, and I was able to get a good export after deleting some extra nodes like this. However, saving and reopening the project broke the export again. Also tried exporting to .mp3 and .wav, different bit depth and sample rates, checking and unchecking all possible export boxes, nothing makes a difference. It's a frustrating bunch of trial and error whenever I need to export, and I have never been able to get past this at all in CbB. Splat has been the only possible export when this happens and even then it's a guessing game that doesn't always yield results.
 
Again, never any problem during playback. The projects always playback perfectly, even if I hit play right after a bad export.
It's difficult to post example audio as this is a client's project that I'm mixing.
 
I can't be the only one stuck on this, and it's a pretty big problem if the exported project is different from the playback, whether it's subtle (one clip gain automation not exporting) or striking (big reverb tails cut off). I've been a Sonar user in a professional recording and mixing capacity for a long, long time, and have never seen anything like this before.
 
Anyone have a clue? Any ideas appreciated.
 
Thanks All.
 
Tech details:
CbB current version
Splat 23.1.0 build 32
RME Fireface UCX latest drivers
Win 7 Pro x64

Thanks GIM but I think this is a different issue. I don't get any kind of error, just an incorrect export.
 

These are my export settings and they have always worked > I always use "SELECT NONE" before export. This picture is from my tutorial found in my signature. 

There are reasons I have always used "select none"  
 been so long I forget why. But it was someone on this forum told me to try it a long time ago when I was having a problem with export. Since that day all my exports have been perfect. , well technically speaking.. 
 
The end of song issue is often complained about. Sometimes it's a volume envelope. 
Are you saying your problem is reverb tails cut off at the end of the song? or is this throughout the song? 

A few suggestions:

• Increase buffer sizes for mixing and editing. Change them back if necessary for the recording stages.
• Make sure that "Fast Bounce" is unticked.
• Archive any tracks that contain audio or midi clips that are no longer used in the project.
• Temporarily archive tracks that are muted and not part of the mix.
• Export as 24-bit with dithering turned off. Convert the exported file to 16-bit as a separate stage afterwards.