Layers added to map not visible in 3D map mode

Layers added to the map from a WMS service are not visible on the map when switching the map to 3D mode. The service requests are converted to proxy requests by adding http://localhost:8080/geonetwork/proxy?url= in front of it and get a 500 error status result. In 2D mode the services work without problem but switching the map to 3D mode makes them invisible as the layers can not be loaded through the proxy url.

Steps to reproduce the behavior:

1. In User interface settings turn on the option 'Allow 3D mode'
2. Go to the map and add a layer through Add Layer > Services, for example: https://geodata.zuid-holland.nl/geoserver/landelijk_gebied/wms
3. The layer is visible in 2D mode. Then switch to 3D mode by clicking on the button 'Switch from 2D to 3D'
4. Now the layer is not visible anymore. The F12-menu shows the proxy requests with 500 errors.

Test environments:

• GeoNetwork 3.12.11 server installation opened with Chrome on Windows
• GeoNetwork 3.12.10 Docker installation opened with Safari on Mac OSX

Reproduce the issue by enabling 3D mode, adding the example WMS service, and switching from 2D to 3D. Start by inspecting the proxy requests shown in the browser's F12 menu; done means the WMS layer remains visible in 3D mode without 500 errors.