Random bugs with extensive use of Transform Effect
I happen to have linked files (typically PNG files) inside a group of objects.
A Transform Effect duplicates the group.
Effect > Distort & Transform > Transform
Here, I typically set a certain number of horizontal and/or vertical move and a number of copies for the whole group including a linked PNG.
(Actually, this is a way to bypass the issue of library symbols that cannot include linked files.)
Every time I open the AI document, the original group is visible, the duplicate groups can be seen, but not the linked PNG inside the group, both in the original group and the dynamic duplicates.
(If I export the document to PDF, the image is also hidden.)
To make the PNG visible, I need first to either double-click the original group (until the image appears), or just move the group around.
It doesn't happen with all linked PNGs inside duplicated groups, but if it happens to a PNG file, then it happens every time with this specific PNG in this specific group.
The PNG files have nothing special, to my knowledge.
They are stored on my hard drive (synchronized with Creative Cloud).
They are usually at screen resolution, so not so big in file size.
I've made a test. I took one of the documents having the issue, and saved it as a new AI file, after removing most of the artboards and contents, keeping only the ones with the duplicate group for testing purposes.
When I open this test file again, the PNG is displayed properly right away.
If I do the same (i.e. re-save the AI file), but without removing unnecessary artboards and contents, then the issue remains.
It makes me think it probably depends on the document overall complexity.
I have another such document, in which I make an extensive use of the Transform Effect, with groups duplicated across artboards. It also has 2 instances of the PNG issue. Actually, the whole document seems to have become sort of "corrupted" because of one of the duplicate groups, it seems (not even one of the buggy groups!). I cannot save the document anymore unless I disable the Transform Effect from the Appearance panel. (the group is duplicated 45 times, 9 horizontally & 5 vertically, and it's been working fine... until it didn't! no idea why... but it's really document-related).
An Adobe Community Professional tried to replicate the issue, but he couldn't.
Windows 10 Pro / Illustrator 23.1 & 24.0 / 64bits
(the PNG bug seems stable across recent versions of AI)