The footnote text is missing when generating a PDF report for both order and invoice. However, if I only generate the HMTL version, the footer information can be seen. 

I am currently using Odoo Enterprise 16 installed on Ubuntu 20.04.5 LTS
with wkhtmltopdf 0.12.5 (with patched qt)

I already tried to use different versions of wkhtmltopdf, which also didn't work and also tried to set the record report.url as seen in the video: https://www.youtube.com/watch?v=lC9p_QJUW1Q

If I want to generate a sample preview, it looks fine including the footer, however if I generate the final pdf the text of the footer is missing.

Edit: 
Solved issue by deactivating debug mode as stated in ir_actions_report.py:
# Disable the debug mode in the PDF rendering in order to not split the assets bundle
# into separated files to load. This is done because of an issue in wkhtmltopdf
# failing to load the CSS/Javascript resources in time.
# Without this, the header/footer of the reports randomly disappear
# because the resources files are not loaded in time.