Hello @EmT I am here representing a client that uses your products, we have recently updated Affinity Designer from 1.8.5 due to some stability issues with documents to 1.10.5, it has solved the stability issues but now we're having similar problems described in this thread (I have also tried 1.10.1 and it has the same issue).
Essentially exporting to PDF or SVG always exports wrong colors with gradients, I have included a document you can experiment with that only has public information and an example of the issue exported to PDF.
We would go back to 1.8.5 but some documents have already been started with 1.10.5 and they do not open on older versions so we really need this fixed, it's a very common use case for this client. We're currently getting around it by exporting to PDF flattened but that is not a long term solution in any way, it loses quality, the ability to select text and the file is huge.
Here's an example of how it should look like (flattened and in Affinity Designer):
And here's how it looks exported to PDF normally without flattening:
As you can see the colors are completely wrong and sometimes it even export partially right and partially wrong like the thread author's example.
Hope you can help.
PDF EXPORT FLATTENED.pdf
PDF EXPORT FOR PRINT.pdf
DOCUMENT WITH ISSUES.afdesign