Welcome to printing with ABS. I avoid ABS because of various issues, but no one else seemed to be answering your question.

ABS has a fairly weak layer adhesion, and layer separation is one of the challenges of printing with it. The issue is that uneven cooling causes stresses than can lead to warping, popping off the print bed, or layer separation. An enclosure for the printer that minimizes drafts and helps keep the print warmish to completion is the best answer. More perimeters or adding/increasing infill is something you could try. Maybe a bit more nozzle temp in order to get as much layer adhesion as possible?

I've seen cracks appear or get more significant in the week or so after an ABS print was completed.