Text in fillable field vanishes despite correct formatting

Hi everyone,

we're experiencing problems with a fillable PDF.

We provide our customers with a form, that they need to fill out and send back to us, usually via email.

The fields in this fillable PDF are all correctly formatted. The text in each cell adapts in size when getting too long. Yet now and then our customers send the PDF back to us and the text in some cells didn't adapt in size. Instead it vanishes to the right, as if the font size wasn't set to automatic.
Is this due to the programm our customers use to fill out the PDF or can settings get lost by sending the form via email?
Thanks for your help