I have identified an DNS problem on my OPNsense:
# nslookup markdownifier.devontechnologies.com
Server: 192.168.3.1
Address: 192.168.3.1#53
Non-authoritative answer:
Name: markdownifier.devontechnologies.com
Address: 0.0.0.0
just now with google dns:
# nslookup markdownifier.devontechnologies.com 8.8.8.8
Server: 8.8.8.8
Address: 8.8.8.8#53
Non-authoritative answer:
Name: markdownifier.devontechnologies.com
Address: 66.39.100.167
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 devontechnologies.com.
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.
Excellent!
Thanks for the follow-up and diligence. Where you ended up is where I was leading. 