Shifting pitch roughly 7 minutes into a recording

I am not an expert on audio or editing, so I apologize in advance if this is not as accurate as it could be.

I have used audacity 2.1.2 for several months now to flawlessly record audio for my podcast. For the last 3 episodes, at some point (usually 6 - 7 minutes into my recording) the audio shifts in pitch. So, when I listen to the finished recording, it sounds perfectly normal through the first 6 or 7 minutes but then magically shifts to much lower pitch. I sound like I have a much deeper voice. I can fix this by going in and splitting the track at the change and shifting the pitch back up, but why is this happening. Any help would be appreciated.

Using a Yahama MG10 mixer to record into an HP Pavilion running Windows 10 and Audacity 2.1.2.

Audacity 2.1.2 is very old. The current version is 2.3.0 (Audacity 2.3.1 is due to be released in January). You can get the current version via the Audacity website: Audacity ® | Downloads

How is the mixer connected to the computer?