That was sample #21 - They just updated the Samples page (see: https://mars.nasa.gov/mars-rock-samples/#21)

Pilot mountain was cored on sol 882, but no capping / sealing was imaged until 913. I believe this was a repeat issue that they experienced earlier in the mission with another sample. We've experienced several 'Quite Days' where the rover did very little after they cored Pilot Mountain. I am assuming that those quite days were attempts by the team at JPL to understand more about the capping / sealing issue. Hopefully they have bottomed out the issue, else we could expect to see more delays like this...