There was a video on youtube about wrong seat cushions recently. Basically as I understand it a certain approved size of cushion is needed and on some aircraft non compliant cushions were installed. I guess thats why.

Edit to add - this is what I was thinking of, in this case on a LIN-LHR it appeared Italian spot check found wrong seat cushions.

https://www.paddleyourownkanoo.com/2024/02/08/british-airways-flight-delayed-after-italian-aviation-officials-discover-some-of-the-seat-cushions-were-too-thick-no-really/