I can reproduce this issue with 2 elements being somewhat consistently invalid, but interestingly enough, the 2 indices in error seems to change from one trial to the next. I am quite confident that the ordering in the Java List is the same each time, so I'm not sure why it wouldn't be the elements at the same 2 indices each time that have an issue.
You can see that _sj_root_516091402 is the main object returned when it is eval'd.
On line 1072, this main root object is set to _sj_2020112488.
Doing a search for _sj_2020112488, you can see that almost all of its indices are set to RoutableForm objects (which have attributes activityName, formNumber, routesToRoleName, formName, formDescr, and categoryName). However, if you look at _sj_2020112488, you see that it is set to a Category object instead (which has parameters name and desc, along with an array called "forms" that is empty for all Category objects currently).
This Category object should not be directly in the main array. I would expect an individual RoutableForm object in the array to have a reference to it, but it should not be directly in the main array.
Don't know if this is relevant, but WAS 6.1 on Windows XP