Phantom Ringing with video doorbell 2nd Generation

We replaced our old (analogue) doorbell with a second-generation video doorbell.
Installation went fine, the doorbell charges and when the button is pressed, the gong starts to ring.

Unfortunately, the gong is ringing intermittently as well when there has been no interaction with the doorbell. Since deactivating movement detection, the phantom ringing has appeared 5-10 minutes after the doorbell has been pressed (each time it rings multiple times without any apparent regularity over several minutes).

The doorbell is connected using the pre-existing wiring to the Schneider Electric 8VA bell transformer (ITR ta35/E) on the distribution board.

The gong is currently configured as a mechanical chime.

What can I do to resolve that phantom ringing?