Why do I get the warning "No thumbnail indexed" in search results?

There are multiple reasons for this. Initially we had a problem with different file formats for the Sentinel-2 data we indexed. This caused trouble in the SAFE to NetCDF conversion. This issue is fixed. When this appears now it is related to the performance of the WMS server supporting the indexing. In order to handle the large volumes of data, the communication with the storage backend has been reconfigured. This reconfiguration is not fully completed yet and causes these errors currently