I was facing the same thing as OP. Based on some of the comments, I went into UBO and turned off Adguard Other Annoyances filter. And that worked.
Firefox
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Reader View is working for me with that website. The only issue is that it writes out the phrase "link opens in New tab" after every link.
Do you have cookie settings or extensions that might be interfering with something?
I think the only extension that does anything with a sites content is UBO. I could try that I guess? Edit: Goddamnit, yes that did it. I'm so not turning off my adblocker for their fluffpieces. Thanks.
It's weird for me. I get the cookie bullshit in reader view, but if I refresh it then I see the article. This happens with uBO enabled or disabled, either way.
Yay the astronaut sloth! I haven't seen this in quite some time online.
Open the cookie page in reader view then refresh the page (mobile/desktop). It fixes it!
I'm using Librewolf with UBO (with all filters on, including annoyances which are not on by default) and the site looks fine in reader mode and normally.