Cracks in new-ish plaster - use solid or flexible filler?

[KE55]

We had our bathrooms refitted about 9 months ago, which included re-skimming the walls. I just noticed a crack has appeared near the top of one wall.

I spoke to a plasterer and he recommended using a fine non-flexible filler. However, elsewhere I've read it's better to use a flexible filler like caulk.

I don't know if any further movement is likely. Any suggestions on which type of filler to use (or any other advice) would be welcomed.

 

[Pigeon85]

Fine filler is correct, open up the crack a little bit more and fill.

Caulk is more for bridging a gap between two different materials. ie between skirting and wall.

Using caulk in a crack like this will shadow under the paint and stick out like a sore thumb.