In case it randomly starts failing now and someone wonders why: ista just had updates installed.
It was also rebooted to fix the ‘long running buildslave forgets to ask for new work’ issue. Note: I’m not actually sure which side (master/slave) the issue is on, but restarting the slave usually fixes the issue. If a machine has been running for several months, the delay between finishing one build and starting the next sometimes gets really long and only restarting the buildslave process fixes it.