I'm not able to reproduce this behavior. LR 7.0 had some bugs with stacking and export, but these were supposedly fixed in 7.1. It would be great if you could make a full-resolution screen video of the exact steps you take to make this occur, and then file a bug report in the official Adobe feedback forum: Lightroom Classic CC | Photoshop Family Customer Community
I tried it again and I was also not able to reproduce it with the steps above. However it happened again yesterday and I have discovered that it is the act of importing new images to a collection rather than closing and reopening Lr which causes the issue.
So here are the steps:
- I rate my images to filter them for editing. I rate the ones that I want to edit at 4 stars and then set a filter for ≥4 stars. Everything else is rated at 2 or 3 stars and is therefore not visible any more.
- I do some basic Lr edits on the filtered photos.
- I open each in an external editor, editing a copy with Lr adjustments. (in this case Portrait Pro, in my previous case it was Photoshop CC or ColorEfex). When the image is saved and I am back at Lr, the new copy is in my collection stacked with the original and has inherited the original's 4 star rating.
- I rate the original at 3 stars to remove it from my filtered view.
- When I'm finished, most but not all of the images from the collection with 4 stars are the externally edited copies.
- I import a new set of photos to the same collection. These are unrated and so I do a rating pass on this import as before.
- I set a filter for ≥4 stars and now, I can only see the most recent import and any of the previous import that were not edited in an external editor. None of the externally edited images are visible.
- No matter which filter I set (or no filter), I cannot see my externally edited images in this collection.
- I go to my Smart Collection and see that the externally edited images are visible in there. I select them all and the context menu gives me the option to add them to my target collection (I have previously made my current collection the target collection). This is only possible if the images are not already in that collection. If they were, the context menu would give me the option to remove them from my target collection instead.
I can reproduce this 100% of the time.
For others reading this, the conversation is continued in the official Adobe feedback forum: Lightroom Classic: External Editors and Collections | Photoshop Family Customer Community . Please don't reply here.