At the time you did post that accusation against a moderator, the only moderator post in this topic was by jfb, and jfb did just state that DNS is working, which could hint at client-specific issues, so I don't know where you got that idea that you are the problem.
It seems unfair to me that you are turning your own words against us, and I can't help noting a tendency of yours to read comments negatively, even if they are not directed at you.
Your title makes it clear that you suspect DNS to fail, and you seem to be reluctant to accept that DNS is not the issue, despite your original post already demonstrating successful DNS resolution.
It would not be unexpected that DNS replies may differ over time or by requestor, and there are several reasons for this.
It is common that DNS may hold several IPs for the same domain, and authoritative DNS servers may shuffle them in their answers to distribute load, or to pick only the one they'd deem topologically closest to the requestor.
Also, as a recursive resolver, unbound would be talking to authoritative DNS servers, whereas a public DNS server may serve answers from its cache.
And DNS records may be updated by authoritative DNS server's maintainers at times, in which case public DNS servers may lag behind authoritative ones for as long as the previous record's TTL.
But even as returned A records can differ, DNS has successfully completed.
If your machine cannot connect to an IP in time or not at all because the servers are under heavy load or down, then that's not a DNS issue.
Primarily, it indicates that there is no issue with DNS in general, be it Pi-hole, unbound or public resolvers.
Your issue is connectivity to startpage.com servers.
As noted before, contrary to your title, you've demonstrated that unbound has no trouble resolving www.startpage.com at all.
If other users can confirm startpage connectivity issues, you should probably seek information and advice on startpage outages.
After all, this is the Pi-hole forum.
We can help you analyse and fix DNS issues, and probably tune your home network a bit, but a public IP being unresponsive or inaccessible is simply beyond us.