It seems that certain conditions may cause imaging to go haywire.

To reproduce this:

• installed the EE 4.3.7 bundle (me, with Postgres PM)
• surfed the demo site, go to "Multimedia"->"Image Gallery"
• click on a magnifying glass

Activity monitor under OS X shows that the org.apache.catalina.startup.Bootstrap process starts eating up CPU (see first attachment). If you click on one of the magnifying glasses on the page in order to get the high resolution images, the lightbox-like overlay does show up and works, but shows no images (see second attachment).
Leaving the page doesn't help.

Please refer to third attachment for a thread dump.