On 23 Feb., Pal. ops. attempted to fire an HMR ["home-made rocket"] from Sheikh Zayed City toward the Green Line; it exploded at the launch site.So the rockets to Ashkelon on the 26th were not done in a complete vacuum.
This might also explain why Israel closed Kerem Shalom for six days in response to the Ashkelon rockets - it wasn't only that attack but also the earlier one that showed that the truce was fading, and (I assume) the IDF wanted to send a stronger message than usual that going back to the status quo of occasional rockets is unacceptable.