After almost the entire day fiddling around with code, I worked out that it required the placement of a single "." in some shell script to solve a rather bizarre malloc error introduced yesterday when I updated glibc trying to solve a possible mathematical error in another package entirely.
I'm vaguely unsure why this extra "." is needed, since the code has worked fine for almost a decade, but I'm just happy that I sorted things out before the next deluge of data downloading was due to commence at midnight.