The user cannot open it
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What people actually do
Leave the cap resting on the bottle, decant into a plain container, transfer a week of doses into something open, or ask somebody else to open it and then not close it properly. Every one of those is a worse outcome than an ordinary cap would have produced.
Which is why 90 percent is in the standard
The senior adult use effectiveness requirement exists precisely to stop manufacturers solving the child test by making the package impossible. A design that fails that threshold has failed, not compromised.
Hand strength and arthritis are the common cause
Push-and-turn needs simultaneous downward force and rotation, which is exactly the combination arthritis makes difficult. The population most likely to be taking daily medication overlaps heavily with the population least able to perform that action.
The one-minute retest is where this shows
Somebody can usually solve a mechanism given five minutes. Whether they can then repeat it in a minute is what predicts whether they will manage it every morning, and it is the part of the protocol that matters most for this failure.
Consider whether you need it at all
If the product is not required to be in special packaging and the household has no children, a reversible cap or an ordinary one may serve the user better. Fitting a CR closure because it seems responsible, to a product that does not need it, can reduce real-world safety.
Instructions on the cap, not in a leaflet
The molded arrow or text on the closure is what somebody reads at the moment they need it. A clear one is a meaningful part of the design and a faint one makes a workable mechanism feel impossible.