Great question — answering as the UphillTech team:
To answer your question: no, looks like that's not the cause. It wouldn't be the tracking parameters because you mentioned that some conversions are being picked up, and others not. If it was the parameters, it'd be absolute: either always worked, or always broke. I think there's something wrong with your GTM/pixel or the SPA itself. I recommend that you have a developer look into it, and use Facebook's server-side conversion tracking. https://developers.facebook.com/docs/marketing-api/conversions-api/
Full answer by DHB: https://webmasters.stackexchange.com/a/131533 (CC BY-SA 4.0).
Need it done for your business? UphillTech.
