Niantic discovered a bug in Prime version 2.21 after they started rolling it out. It wasn’t a big deal though because it only affected agents ability to make links:

Agents, we discovered a bug in the Ingress Prime 2.21 release that affects the ability to make links. We’ve decided to stop releasing 2.21 and roll features and bug fixes from this release into 2.22. Thanks for your understanding!

— Niantic Support (@NianticHelp) April 25, 2019