OK, that worked. Thanks.
I started up Chrome and navigated to various pages - terrarium, inventory. I did notice some broken links - and when I looked at my trace log, I saw that we had fetched the files and the browser later asked for those same files with "If-Modified-Since". KoLmafia send bak "Not Modified", on the assumption that if we had it cached, the browser must have had the file. Apparently not.
I didn't have a full debug log, so I don't know what Modified-Since date it was asking for.
Revision 12641 actually compares the "If-Modified-Since" date to the the lastModified date of the file. If the file is newer, it sends the file (again). Otherwise, it says Not Modified.
I was unable to reproduce the problem after doing this. Actually, I was unable to reproduce the problem BEFORE doing this; only the first try actually had any broken images. So, I don't know if this fixes your problem, but it's the only suspect behavior I was able to observe.