I made some progress. Since I didn't have the whole matching L5K file, I stripped down the crimson file to what I did have recreated in my CPU. Until I did that, the Red Lion was complaining about comms loss. So I made a new file with just the OEE Down code entry page and imported the much smaller L5K file from my CPU.
Afterward, I was seeing blanks for text and I could fiddle with the length in Logix5k and even the characters and see nothing on the screen. After attempting to type in "TEST" on the HMI, RSLogix would show the length change to 0 and all null characters and still blank text on screen.
I found that the setting for the string tags under "Packing:" was set to "ASCII Little Endian". I changed that to "None". After doing that, I can write to the strings and see them on screen just fine, but the length always ends up as 12 characters...even with the Entry Complete action set...so either I messed up something or Crimson always thinks the strings are 12 characters long even when empty...
I can think of a slightly ugly way around this, but want to dig deeper...