Playhead position suddenly moving jerkily

After a year of flawless movement, Audition's playhead today started moving jerkily.

For any audio editor to function AT ALL, it has to have some graphical element (Audition's "playhead"), that moves instantaneously along the waveforms, matching the sound being played over the PC to the waveforms associated with that sound.  The work I do in Audition is IMPOSSIBLE without this most basic function.

For the first year of steady use, Audition did this perfectly.  But today, mid-session, it shifted to jerky movement.  Now it jumps position every 200 to 400 ms, then freezes in the new position, motionless until the next jump (200-400 ms later).

This started occurring midway through Audition editing work on a single .wav file today.   One moment the playhead position was moving normally.  The next, it only moves by jumps and freezes.

I had nothing else running on my PC.  I have not recently installed any new hardware, software, driver updates, or accepted recent updates to Creative Suite.  My PC is an overbuilt home build with heavy resources, which has run Audition flawlessly for the last year.  There is ~900 GB free on the main SSD pair (2x1TB SSDs in RAID0).  Audition's user temp files are tiny.  Malware seems unlikely; I use Norton 360 religiously, and was not downloading anything when the stuttering started occurring.

I tried opening different .wav files in Audition.  With one smaller file (a ~2.5 min long mp3), I got a ~1-2 second period of somewhat smoother (but not the usual perfectly smooth) movements at the very start of playback.  But immediately after that, the playhead's movement reverted to all stutters, even when I "rewound" the playhead to start of the file (where it briefly had moved smoother).

So for right now, Audition is dead to me.  This is major concern, since I have many projects in the works.  Any suggestions would be awesome.