I've previously created an editable PDF (funding application form) and i've received a completed form back, however one of my boxes that is used for text (for the applicant to type into) appears blank, until i press on it and the text comes up. It doesn't do this with other boxes and i can't seem to see how i've set it up differently. I've got a character limit on it so not sure if this has something to do with it? (just guessing here).
One of the most unpredictable settings can be the Font size:Auto. If that field is set to Auto, try changing it to a defined point size to see if that changes anything. Just a guess, but might be worth a try.
Another thought is that there might be some extra characters/lines that may have been pasted into that field. The desired text string may be out of view below a bunch of blank lines. Just a hunch, but worth investigating, perhaps.