Exporting to PDF SVG images with gradients

[MaFab]

Hallo, I am new on this forum. I'm using Scribus since three years for creating books with lot of illustration and I am very happy of it. I never had any problem exporting to PDF documents containing SVG graphics including gradients. I work in a  MAC OSX environment. Recently I exported a document containing such kind of graphics but ...it doesn't work anymore! Gradients are converted to plain colours. I cannot understand what could be the cause of this behaviour. The only thing I can think about is that - maybe, but I am not sure - the problem arose after installing Mac OSX 10.14.3 (Mojave). Could someone help me? Thanks!