Version Indesign 2020
Steps to reproduce.
1. Create a document with an index
2. Create styles for the index in a style group
3. Generate an index with the styles that are in a style group
4. Save as IDML
5. Open the IDML
6. Try to generate the index

Expected result: The settings/options in 'Generate Index' are kept as they were in the original file.

Actual Result: The options are reset to the default styles, not the styles inside the style group.