Bon, voici la réponse du support :
Thank you for the inquiry. What packages do you install? It is hard to say which process/packages affect it and need some test in your site to help us narrow down the root cause. Please enable usage history in Main Menu > Resource Monitor > Advance settings. Check if there is convert process running in Control Panel > Media Indexing service > Conversion Settings > view progress or Media Indexing service label, blue texts behinds Re-index button. Please kindly stop all services (System Information > Service > disable all services) and packages, check how is the CPUusage. unplug all external devices including UPS or external HDD, and unplug Ethernet cable and try. Then please enable service/packages one by one, check which service/package is the root cause. Then let us know. Please send us a copy of your (1) kernel log and (2) system log, the instructions have been mentioned in below. The Kernel log is a technical log file which can give us more technical information about your system
Il me reste à faire une synthèse de ces 40 échanges ... et à leur envoyer ...
Je vous raconterai bien sûr la suite ...