The most probable reason - some input pin may be left unconnected and acts as antenna.
The most probable reason - some input pin may be left unconnected and acts as antenna.
It turned out that TEST_MODE pin (D6) was left unconnected, it shold be the reason.
Also, it migh be a failed joint under the package that bounces under the pressure. You can distinguish between two reasons by touching the package by a plastic stick rather than by a finger.