Hi Jon Lewis,
Please have a look at the clip and the file, I hope that will show what happens.
Scene file and clip
https://www.amazon.com/clouddrive/share/XwthkLSPALELr2jM14aRJgf7JdyIzDCLFyGCQtwWg17
In short, your Cloner Object was set to “sort”. Since you have had reduced the scene, I guess this is the missing part, no information to sort things, so the first child was repeated 36 times, hence all in Buffer 1, nothing in buffer 2-33 (34?). 36 clones, 34 child objects
The Options to select all Comp tags seems not to put the Attribute manager to work. So, selecting first one Tag of its kind does this, then RMC click to “Select all ‘Compositing’ “, as shown in the clip.
If there is anything I have missed, please let me know, I’m happy to look into it.
All the best