"InSight was previously scheduled to ship to California in early January, but delivery was moved three and a half weeks early to provide more time at the launch site for the integration of the seismometer instrument (SEIS) developed by the French Space Agency, CNES."
"A vacuum leak detected during testing of the seismometer was repaired last week in France and is undergoing further testing."
Payload Problems May Delay Mars InSight Launch (Update), earlier post
"Consideration is being given to delaying the launch of NASA's Mars InSight lander mission. The problem has to do with the French seismometer. There is a persistent leak inside the seismometer that has been hard to fix."