Thumbnail URL missing base url when installed in subdirectory

[Mark-H]

MediaManager source is configured as follows:

MODX is installed at https://development.local/3.x/, so inside the /3.x/ subdirectory.

That means files should be getting uploaded to 3.x/assets/mm/, which they are. So it's going fine up to this point.

However the media manager shows broken images in both the list and the image preview panel:

The browser dev tools shows 404s for URLs like https://development.local/assets/mm/2023/02/thumbs/c494530a66155f3951db1d0b01f6777f.jpg - so without the /3.x/ subdirectory. The actual file with that hash does exist in the expected location.

Interestingly, the link shown in the preview panel does seem to be correct, so this is purely an issue with the thumbnails from the looks of it.