What about Thunderbolt3 docking bricks? Is there a known problem with recording through a Thunderbolt3 docking brick, where the Focusrite audio interface USB cable is plugged into the Thunderbolt3 docking brick, and the docking brick is plugged into the Thunderbolt3 port on the laptop? Also, are there any known issues with recording to external hard drives via USB 3.0 or Thunderbolt cables? Are there any known issues with disk read/write buffering settings in Sound Forge? Is it possible that there is some kind of read/write buffering problem between the laptop memory and the laptop disk drive?

I tried plugging in the Focusrite audio interface directly into my Laptop USB 3.0 port, and it was able to record fine for 21 minutes before the flat line event showed up in Sound Forge. In the example I showed above, that flat line event came just after 3 minutes. Does this mean anything to you?

I tried recording using Sound Forge Pro 13, and after 21 minutes I get a similar scenario, the flat line buzz sound just appears out of nowhere after recording music just fine for 21 minutes. Same Dell laptop, same Focusrite audio interface plugged directly into the laptop, recording directly to the laptop nVME hard drive. This looks like some sort of software buffer overrun, or disk read/write error to me.

I thought of some other possibilities. What I am trying to do here is basically use Sound Forge, the Scarlett audio interface, and Sound Forge like a DAT machine so I can record long DJ sets. What about other software processes running in the OS background, like virus scan, or iCloud sync, or One Drive sync, or Adobe Creative Cloud, or some other OS processes etc., could these interfere with Sound Forge's processing to record real-time audio to the hard drive? Is there a check list of software that should be turned off or disabled while recording real-time audio through Sound Forge to record directly to the computer's hard drive?

Is your audio interface's driver up to date?

Yes, all hardware, firmware and software drivers are up to date. I am using the latest Focusrite drivers they have. The only thing I can think of right now is going through "a process of elimination", try another laptop, try another Focusrite Scarlett device, try direct cable connects to laptop instead of through Thunderbolt3 docking brick, etc. It will take a while to test out all these possibilities. I would just appreciate some kind of article that talks about the recommended laptop setup, including use of docking bricks, use of external hard drives, possible software conflicts running in the background like virus scan, iCloud sync, One Drive sync, etc. I have not seen anything about what the recommended setup should be for recording long real-time music sets. All these recording problems make me miss my old fashioned DAT machine which was a workhorse and never screwed up.

I had a HHB PortaDAT.. Can't say I miss it very much. If was heavy, ate batteries and occasionally a tape would not playback in other machines.

And then there were rotating heads, head cleaning tapes, formatting gaps on tapes that confused some machines, and digital transfers that had to be done in real-time. Pure joy. 😉

I am 90% sure this is a driver memory leak situation, especially if they are using C++. Memory garbage collection in C++ can be tricky, and my software experience gives me a hunch these symptoms point to a memory leak scenario.