The tag fails near a wireless charger
A charging pad is a coil mounted on a ferrite shield with metal behind it, which is the on metal problem in a different package. Unplug it and retest: if the tag then reads, the active charger was the cause, and if it still fails, the assembly is.
What a charging pad is
A flat coil on a ferrite shield, usually with a metal plate or housing behind it. That sandwich exists to direct the charging field forward and keep it out of the electronics behind.
From a tag's point of view, that is a conductive and magnetically active surface, which is why a tag on or under a charging pad behaves like a tag on metal.
It does this whether or not the charger is switched on, because the shield and the metal are physical.
An operating charger adds an active field and an electrically noisy environment on top of that, which is a separate contribution.
The unplug test
Unplug the charger, wait a moment, and repeat the exact test that failed.
If the tag now reads, the charger was active and its operation was the problem. Charging and tapping at the same time is the situation to avoid.
If the tag still fails, the assembly is the problem and unplugging changes nothing. Then you are dealing with the metal and ferrite, and moving the tag is the answer.
This single test splits the fault cleanly, and it takes a second.
Where this shows up
A tag stuck to a desk with a charging pad underneath, or beside one.
A phone sitting on a charger being asked to read a tag held above it. Both coils are then in play at once.
A charging pad built into furniture, where the pad is invisible and the surface looks like ordinary wood or laminate.
A car with a charging cradle, which combines this with everything else a car brings.
The furniture case is the confusing one, because nothing visible explains why one spot on a desk fails.
Fixing it
Move the tag away from the pad. A hand's width is usually enough and it costs nothing.
Take the phone off the charger before tapping, which is the fix for the phone side of the problem.
If the tag has to stay where a pad is behind it, use an on metal tag, which is built for exactly this kind of backing.
And when a desk or a room has unexplained dead spots, look for built in charging before suspecting the tags.
Frequently asked questions
Does wireless charging damage NFC tags?
No. The charging field does not harm a tag, and the assembly blocks reading while the tag is against it.
Can I read a tag while my phone is charging?
Take it off the pad first. Both coils are otherwise in play, and the pad is a metal and ferrite backing right behind the phone.
Why does one spot on my desk not work?
Look for a charging pad built into the furniture. It is invisible from above and behaves like a metal surface.
Do the two use the same frequency?
They operate at different frequencies, and the problem is not frequency overlap. It is the ferrite and metal in the pad, plus the noise of an operating charger.