Currently, when using External Stylesheets in the reports, the engine tries to first load the stylesheet as an embedded resource of the assembly. If it fails to load it from the assembly, a message is written to the trace along the lines of:

ESS: Attempt to load ExternalStyleSheet from EmbeddedResource from assembly Telerik.Reporting, Version=19.0.25.211 with resource name styles.xml is unsuccessful.

After this, the engine will try other ways to resolve the stylesheet such as from URI and if it succeeds, the report will render as expected.

This can create confusion because looking at the trace, one might think that there were errors with the rendering of the report because the stylesheet did not load but it was actually successfully loaded with one of the other approaches.

It would be better to write the errors to the trace only if the stylesheet does not load after all attempts.