Over 2 seconds audio draft on Wirecast

First, a list of hardware and software:

• HP Z8 Workstation with 2 Xeon Gold processors, 64gb memory, running Windows 10 Professional
• Presonus Studio Live 32SC connected via USB
• Latest Wirecast version; the latest official release, no beta versions
• No capture cards; everything comes in via NDI (except, of course, audio, which comes in via USB)
• 10gb network just for NDI

As you can see, this is no entry-level system. Now, on with the show.

How do you explain this:

at the start of a 10-hour Wirecast session (no streaming, no recording, timestamps generated by Wirecast, resources well under 20%), just producing on Wirecast and sending the output via NDI), audio was well in sync with video.

A couple of hours into the production (say, about 5 hours), audio started to drift badly. At the end of the session, audio was exactly 2.120 seconds behind video. . I know this because that's the number I had to enter in the video delay box in each of our cameras (via NDI). Yes: the audio was way behind network video cameras.

Why do I suspect that Wirecast is the culprit? Let me correct that. How do I know Wirecast is the culprit? Easy to explain.

At the end of the session, with 2.120 seconds of delay entered, I closed Wirecast. Waited a few seconds, reopened the project and...

Voilà! No audio delay. I deleted the added 2.120 seconds delay and audio was back in perfect sync.

This was also submitted as a ticket. I post it here for two reasons:

• the possibility of this having happened to someone else and already having a solution
• the possibility this happening to someone else in the future

As a well-known song says: "would someone please explain the reason for this strange behavior?"

Thanks for your attention.