Template editing issue : blank template shown

Hi,
We managed to create a template and save it. But when we try to edit it we have a blank page why no data! No way to make any change even on the setting on the top-left corner.

Any idea how to save the pb? We cannot link the template to our form:
Please watch video: https://drive.google.com/file/d/1p4zkTdk76nfanCDUWE2k9PCVl0l6Fx7q/view?usp=sharing

Thank you for your help

The page I need help with: [log in to see the link]