I know that the plural of anecdote is not data, but I know so many people now who've had obvious covid symptoms after known close-hand exposure and tested negative throughout (LFT and PCR) makes me think that we will discover at some point that there's something about omicron that can't be picked up by some tests that catch other variants. Usual caveats: not an epidemiologist and my acquaintanceship is not a statistically significant sample.