Pagespeed: authorized and 4xx status code

[kallehauge]

We are having some trouble with pagespeed and HTTPS resources.
Example where you can see it: https://conscia.com/solutions/?PageSpeedFilters=+debug

Some of our assets do not get processed because of the following messages, when enabling pagespeed:
<!--The preceding resource was not rewritten because it is not authorized-->
<!--4xx status code, preventing rewriting of https://...-->

Looking around the internet it could be related to some of the following:
https://www.modpagespeed.com/doc/domains#mapping_origin
https://www.modpagespeed.com/doc/https_support#https_fetch

... and more unlikely something about certificates but it might be an issue based on the alpine build (we're hosted at Wodby and use Let's Encrypt certificates on the provided website):
https://www.modpagespeed.com/doc/https_support#configuring_ssl_certificates