All part of the Dpf regeneration system. Normal operation.

It means the regen is probably still active when you turn off the engine. On some brands (not sure about Seat) there is a maximum number of times you can do this before the dash light comes on and a garage visit needed and its not a warranty fix.

On our Kia when a regen was close (originally every 300 miles then 250 after a software update) we would check before turning off the engine that the tell tale signs of a regen were not present, if they were we would drive on until we were satisfied it was complete.