Here is a very short memo, simply summarizing information previously recorded in the guestbook.

1. A discontinuity appeared on the Boeing CDU, specifically ROUTE DISCONTINUITY. For example, if a Waypoint at line 3L in the LEGS page is not connected, You can first press 3L to copy it to the Scratch Pad input area, and then press 3L again, and it should connect.

You can refer to this video on YouTube:

2. A discontinuity appeared on the Airbus MCDU, specifically F-PLN DISCONTINUITY. You can press the CLR key in the bottom right corner, and then press the L-side key on the row where F-PLN DISCONTINUITY is displayed.

You can refer to this video on YouTube, the explanation is very clear.