[QGIS-Developer] Missing custom rendering properties in QGIS3 Server

[Sören Gebbert]

Dear developers,
i am trying to use the undocumented custom vector layer property
"rendering/renderAboveLabels" in QGIS3 server with no success.

Storing this property in a QGIS project file enables the rendering of
vector layers after the labeling is done. This works fine on QGIS3
desktop, but not on QGIS3 server. I looked into the server code and
realized that the QGS WMS server uses two renderers
(QgsMapRendererParallelJob, QgsMapRendererCustomPainterJob) of which
one (QgsMapRendererParallelJob) should support the custom property.
However, i can not convince the server to apply the custom property
when parallel rendering is enabled.

What am i doing wrong? Are there differences between GQIS3 desktop and
server in handling project files and layer properties?

Why does QgsMapRendererCustomPainterJob not support the custom
property  "rendering/renderAboveLabels"?

Best regards
Soeren