cannot enter text in a sticky note

Adobe Acrobat Pro (11.0.23) I use on my business laptop licensed by my company, since a year or two. All of a sudden I am no longer able to enter text into new sticky notes. However the security settings (in properties) are set to "no security" all items below on the same page are set to "Allowed". Having done this in the past a hundred times I do not understand where this is coming from. This is now the second pdf in a row where I have this issue.

I can however add a sticky note as such, but then cannot enter text, though the cursor is in the text field ... I just get a tone, no error mesage, nothing.

I am able to highlight text, even text editing is working, but not adding text to sticky notes. see screenshot below.

Help is much appreciated.

Thanks in advance

Eduard