I have identified an DNS problem on my OPNsense:
# nslookup markdownifier.devontechnologies.com
just now with google dns:
# nslookup markdownifier.devontechnologies.com 18.104.22.168
This is definitely a DNS resolution issue with my provider (Telekom Germany).
Their DNS servers do not return any result for the subdomain
markdownifier.devontechnologies.com, they only resolve the main domain
I have now built a workaround by building a DNS bypass in OPNSense, the MD-Export works now well again.
Thank you for your support.
Thanks for the follow-up and diligence. Where you ended up is where I was leading.