In case it may help locate/ID whatever may be causing the attachment pictures to not always/randomly fully display, here are a couple of screen grabs from this morning in
Kevin's (klhansen) Project Journal showing the attachment image thumbnails not all displaying correctly.
Note their are two sets of screen grabs. The first one in pics one and two, then a different set of grabs in three and four. Note that the thumbnails display differently from one viewing to another.

It kinda seems like during the page loading process, there is a minor time delay during the activity that thumbnails load to display. Some load and display quickly, while others take a few seconds to try and load. if a thumbnail doesn't load/display in about 3-5 seconds, it ends up being displayed by the attachment file name link. Those mostly still work if clicked to open and display the full picture, but very occasionally they won't open, acting like a broken link with just a black screen instead of the picture.
I haven't tried to capture that type of event yet, but can if it will help figure things out.
NOTE: This type of picture display issue happens throughout the forums, with posts that have one picture or many, and just random. Sometimes they display, sometimes not???