My website gives "everybody" an error but it works just fine

I have website which runs just fine. I'm visiting it on PC, mobile, tablet and I'm even using Google Search Console & Analytics. And it just runs OK 100%. No issues whatsoever for me.

But when I'm promoting it (like direct Emails, social media etc.) I'm quite regularly getting responses "that website doesn't work" or "that link gives me an error". This issue lasts for months. I checked it on all my devices. I tried online web tests. Checked blacklists. Everything is OK. But...

My website gives "everybody" an error but it works just fine

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