SUMMARY

Vector shapes with gradients in symbol libraries don't seem to load properly anymore, their fill color is just set to solid black.
The black already shows in the preview of the Symbol Libraries docker.
The symbol library itself is not broken, because opening it in Inkscape and copy&paste the symbol into a vector layer in Krita will show the gradient as expected.
It used to work fine in Krita 4.4 at least.


STEPS TO REPRODUCE
1. Open the "Symbol Libraries" docker
2. Choose the "Pepper & Carrot Speech Bubbles" library (a default resource)
3. Look for the "Caption Balloon 1"

OBSERVED RESULT
The speech bubble's main area is black, both in preview and after adding it to a vector layer.

EXPECTED RESULT
It should be a linear gradient with subtle variations of light brown.