NFC works after a restart, then fails again
A software state rather than hardware, because hardware does not recover on its own and then fail again. Toggling NFC off and on is faster than a restart and often works as well, which is a useful clue as well as a workaround.
It is software
A coil and a controller do not fail and then recover on a schedule. A fault that a restart clears is a state that a restart resets.
That immediately eliminates the tag, the surface, the case and the distance, none of which are affected by restarting a phone.
It also means no amount of work on the deployment will fix it. This is a device problem and it belongs with the device.
Toggle instead of restarting
Switch NFC off in the settings, wait a moment, and switch it back on. On many devices this restores function without a full restart.
If toggling works, you have both a faster workaround and a narrower diagnosis: the NFC service is getting into a bad state rather than the whole system.
If toggling does not work and a restart does, the state sits deeper, which is worth noting if you report it.
Either way, keep the quick settings tile available so the workaround takes seconds rather than menus.
Find the pattern
Note when it stops working. After a certain length of time, after using a particular application, after payment, after the phone has been asleep, after a battery saving mode engaged.
Battery saving is a common trigger, since some devices restrict NFC under it and the restriction persists in a way that looks like a fault.
An application that uses NFC and does not release it cleanly is another candidate. If the failure follows a specific app, that is the strongest clue available.
A week of noting the circumstances is worth more than an afternoon of trying fixes, because without a pattern there is nothing to report and nothing to avoid.
Living with it
Keep the phone updated, since this class of fault is fixed in system updates rather than by anything you do.
Report it to the manufacturer with the pattern you found, which is the only route that reaches whoever can fix it.
Do not build a deployment around a phone that behaves this way. Test on healthy devices, because a flaky phone makes every other fault impossible to diagnose.
And avoid factory resetting on a hunch. It occasionally helps, it costs a day, and the pattern you noted is worth more.
Frequently asked questions
Could this be a hardware fault?
Unlikely, since hardware does not recover on its own after a restart. A fault that a restart clears is a software state.
Is toggling NFC as good as restarting?
Often yes, and it is much faster. It also narrows the diagnosis to the NFC service rather than the whole system.
Which apps cause this?
There is no general list, so noting which application preceded each failure on your device is the useful evidence.
Will a factory reset fix it?
Sometimes, at the cost of a day. Try updates, the toggle workaround and a pattern report first.