QGIS » QGIS Application

If multiple map themes are created using different styles for the 1 layer, and Print Layouts are created using the "follow map theme" option, the Legend incorrectly shows styles as per the theme currently being displayed in the Map Composer, not as per the Map Theme chosen in the print layout. This glitch can be overcome by selecting the appropriate Map Theme in the Map Composer each time a Print Layout is to be exported, however, it prevents the use of automated Print Exports for multiple layouts, and introduces significant chances of error by forgetting to update the Map Composer every time.

For example -
See attached images, where I have saved 2 Map Themes... "No Style" and "Categorised".
I then create a Print Layout and set it to follow Map Theme "Categorised". While the Map Composer is showing the same theme, the legend displays correctly. However, if the Map Composer is switched to a different Map Theme, the Legend in the Print Composer no longer reflects what is being shown in the print layout, and instead reflects the Map Theme of the Print Composer.