Admin media selection on page designed fails in production

In the page editor when I click on a widget to select an image the images fail

They're requesting the

.../cmsctx/pm/72d516d1-d705-451e-ac34-c9d650a124e0/culture/en-GB/wg/947bdd8b-315c-4dd2-90a9-f20e0a6b60d3/readonly/0/ea/1/h/89b9952a9cc1c331bf9195199783572653bfec696d1a94ceca47491738be3f5c/-/getmedia...

address, this 500s though with several errors (The site is a Azure App Service, run as package)

Could not find file 'C:\home\site\wwwroot\App_Data\AzureTemp'.

Page builder is not initialized. Use 'IPageDataContextInitializer.Initialize' method first in you code before Page builder scripts registration.

This is response from Microsoft:

With Run From Package, this is strictly enforced as the wwwroot folder becomes read-only. You can still write files to the %TMP% folder if you need temporary storage. But you cannot save files to places like App_Data (but really, you shouldn't be doing that!)