Hello,
Conclusion of this issue:
I contacted Norton support, very friendly, :
1/remote assistance with technician level 1
2/ remote assistance with technician level 2
3/ remote assistance with technician level 3 specialized on virus removal >>> he did not find any malware on my PC but cannot solve the problem.
Norton was not compatible with this PC (1 of my 4 PCs), but the reason stay undetermined.