For what it's worth I think I found the problem. In my configuration.h file I had the following three lines uncommented. I don't recall why but after commenting and disabling their function the twitching issue is gone and the motors move normally again.
#define ULTRA_LCD
#define SDSUPPORT
#define SD_CHECK_AND_RETRY
I'm not sure what the third option does, but that could explain the periodic nature of the issue/interrupt I was seeing.
#define ULTRA_LCD
#define SDSUPPORT
#define SD_CHECK_AND_RETRY
I'm not sure what the third option does, but that could explain the periodic nature of the issue/interrupt I was seeing.