Do anyone have any idea what the cause of this could be, or anything that we should investigate further?
After a long day of debugging dojo code to try to find the problem I finally found what the issue was. Like the post I linked in the original post I had an issue with how the parentLink of the content provider items were set, but in a slightly different way.
The issue was when I was setting the parentLink of the items in my content provider I set the parentLink like:
parentLink = new ContentReference(parentId, providerKey)
For the items in the root level of my content provider the parentId was the ID of my content provider's entry point, but since the entry point (a content folder in my case) was a part of EPiServers "regular structure" and not my content provider's structure this created a problem when the parentLink was generated using my providerKey. I changed this so that the parentLink for the root level items was generated using:
parentLink = new ContentReference(parentId);
Which seems to have solved the problem!
I'm developing a custom content provider which contains images in a folder structure from a third-party service. To make the content provider content show up in the default select-media-dialog I've placed the content provider root as a child of GlobalAssetsRoot and made the component inherit from MediaComponent.
The content provider folder structure shows up in the select-content-dialog but when I click on an image from the content provider the dialog scrolls instead and the image isn't marked as selected. It seems like the image is selected however since the image is added to the property if I click "ok" in the dialog after I've clicked on an image, even though the selection doesn't show up in the UI.
Adding the images using drag and drop functionality works.
It looks like a very similar problem has been discussed before at https://world.episerver.com/Modules/Forum/Pages/Thread.aspx?id=184441 but the solution in that thread doesn't seem to apply here. Does anyone have any idea what could be the problem?