DFPlayer "SerialWrongStack" error : what does it mean ?

Hi !

I use DFPlayer on one of my projects (on a small PCB, driven by a Seeeduino Xiao). The circuit is very simple, and I already produced 10 pieces.

But on my last sample, I encounter a strange error : I get “Get wrong stack” error (when I use the test code from DFPlayer wiki page).

All contacts are OK, the PCB are produced by JLCPCB (not homemade-PCBs), same operating mode.

The test code shows the DFPlayer is online, but I got timeout error and “get wrong stack” error.

The documentation doesn't explain the purpose of this error code, do you have any idea ?

Thanks