It looks like you might be getting too much heat in the neck area. If you notice the area in the next is pretty small so a lot of heat can build up there. Do you have a fan on your printer? ABS likes being kept warm while printing, but I noticed having the fan on can help for narrow/small areas in a print.

You didn't mention the name of the brand, but 240 C is pretty high for ABS. Have you tried playing with a lower temperature? Maybe try starting at 220 and going down, or up depending on the results, in increments of 5 to 10 degrees.