Problem when combining form date field disappear

[Peter15C2]

When combining two filed out and signed (locked) PDF forms the second file to be selected the date field disappears.

Pre-combine:

Post-combine.

 

[Bernd Alheit]

How does you combine the files?

[Peter15C2]

I'm using Adobe Acrobat DC and have tried using both the combine tool and the organise tool

[try67]

Is the first file an Adobe Sign form?

[Peter15C2]

They are both PDF Forms which get filled out by a customer and then signed using Fill & Sign. I then want to combine into a signal document.