Sounds like someone did a bad job managing their maintenance schedule (via Google Translate):

  Can you say anything more about what caused the planes to be grounded?

  "A routine check was not completed within the specified timeline, leading to the decision to temporarily decommission the aircraft. There is no immediate risk, but according to the regulations, these checks must be carried out.

And someone else did a good job not sweeping it under the rug

Yes, they did the right thing.

English translation https://www-nrk-no.translate.goog/norge/sas-kansellerer-flyv...

18 out of 37 neos. So seems like some sort of failure in their maintenance process.