@Callum Well, it didn’t occur with Pdfs from other software, yet. And no, the Jpg generated from the same file was displayed well, just as a pdf of a second artboard where I used the same content, but to keep things simple, except for the type rasterized to a single layer. Neither is the effect shown, when I export an Eps from Affinity, and in Illustrator open and safe it as a Pdf – but then, any effects that might be involved are rasterized on that process, too.
I suppose the effects might be involved, as the foggy area includes a “notch” around the yellow candle, probably because of the gaussian blurred shadow beneath.