My express travel card doesn’t always work

On transport for london my express travel credit card does not always work. Sometimes I can hold my phone above the sensor and the gates automatically open, other times nothing happens. This means that I have to manually select a card from my wallet causing anxiety-inducing hold ups at the gate, plus the occasional ‘incomplete journey’ if I select the wrong card, and its attendant admin hassle.

I have checked that the ‘Express Travel’ option has been correctly selected in Settings.