Form fields allowing user to type text more than the size of the field

I have been creating forms for my workplace which have recently been published online for the public to use.

When creating the forms, I tried to make sure that any boxes that allowed multi-line text did not exceed the size of the box, did not create a scroll bar if too much was written, and did not make the text size smaller if too much was written.

After testing different properties on the form fields, I found that this worked: size 10 font, Open Sans font, check spelling ticked and multi-line ticked. I specifically disabled scroll long text and made the font a certain size so that I wouldn't get the issues about. After testing multiple times on Adobe Acrobat and also in Google Chrome (to make sure the properties translated when a PDF was opened elsewhere), I didn't find any problems.

However, my work has now received two seperate forms where the form fields with these properties are not working in the same way they did for me. For example, on one of the forms a user typed a line that went all the way to the right side of the box and the box cut off the text instead of going onto the next line. The other form did not have this problem, but instead allowed the user to continue typing past the bottom of the box, showing a line of half cut-off text. When I opened this form to see what had happened, I copied the contents of the field (ctrl-A) to a word document and found that somehow the user had entered text more than double the size of the field.

On both instances I opened a blank version of the form they had access to on our website in Microsoft Edge (and had previously checked on Google Chrome) to replicate what they had entered and see if I had the same issue. I also asked a colleague to do the same. Both forms worked as they should and I cannot figure out what has gone wrong.

Is anyone able to figure out the problem here? I am eager to find out as soon as possible because if it's a mistake on my end I will have a fun few days ahead of me!