kasky1, I think you found the issue. Thank you!
Cantai exports as silent files if you export flows as separate audio in Dorico.
If you export the entire project it will export correctly.
A bit of a pain but you can export them as separate audio if you do one at a time via the check boxes. They seem to line up without a problem when importing into other apps.
— Jim
Yes, jaskabong, you can export Cantai parts as separate audio files if you export the entire project as one audio file, not as separate flows. It works as a stereo mix or separate audio tracks. It just won’t work if you export individual flows.
Correct. I have only needed one flow myself but have read that multiple flows are problematic. For export, you may need to duplicate the file and cut down to one flow at a time as well. (As I said before, a pain — now a giant PITA!) 
Yes and no. If you want to export individual flows, you have to move the flow that you want to export in front (before) all other flows in Setup mode. This is a known issue that the development team is working on for a future update. I’m glad this worked for you.
Someday I’ll try to get up to speed on these things that I’m not needing! Being retired, I find I don’t have time for all the things I want to do (despite the GNDN* thing)!
(*from Star Trek lore — labeling on some pipes, stood for “Goes Nowhere, Does Nothing!)
Happy birthday, @jaskarbong!
I’ve had similar issues - when I tried exporting audio for a 6-part piece (SAATTB), various parts started dropping out after a minute or so. But when I exported each voice individually, I was able to put them all together in Cubase and it all worked fine.
And for this particular piece, it’s good to have the individual parts for singers to practice, anyway. But it would still be nice to be able to export everything at once, of course.