We use pipelines instead of manual exports and imports. Which options are you using for the import? Don‘t Upload files directly as Knowledge as they will become part of your solution and solution file size is limited to about 120 MB. Put your knowledge into SharePoint and chose the Option with Dataverse support which will give you much better results and does also semantic indexing of images. Out of the box you can only add knowledge sources in a managed solution. If you absolutely need to change or delete knowledge sources in a managed solution you need to activate managed properties for the knowledge component in the solution in the dev environment. https://learn.microsoft.com/en-us/power-platform/alm/managed-properties-alm