On my computers the shutdown takes between 10 to 30 seconds.
To reproduce the error I installed LibreELEC (official): 9.95.5 10.0, kernel: Linux x86 64-bit version 5.10.41 in a virtual machine OOB and added the Zatoo PVR client from the library. The shutdown/restart tooks the normal time. As soon as I configured username and password and restarted the VM the shutdown takes some seconds sometimes longer. If the addon is showing some live tv content the screen freezes and the shutdown sometimes takes 20 to 30 seconds.
I'm attaching the debug log which contains the following lines:
2021-07-22 10:56:27.551 T:636 INFO <general>: PVR Manager: Stopped
2021-07-22 10:56:27.551 T:636 DEBUG <general>: Destroy: Destroying PVR add-on instance 'Zattoo PVR Add-on:connected'
2021-07-22 10:56:27.598 T:670 DEBUG <general>: AddOnLog: pvr.zattoo: Update thread stopped.
2021-07-22 10:56:35.527 T:636 INFO <general>: Skipped 2 duplicate messages..
2021-07-22 10:56:35.527 T:636 DEBUG <general>: SECTION:UnloadDll(/storage/.kodi/addons/pvr.zattoo/pvr.zattoo.so.19.7.9)
2021-07-22 10:56:35.527 T:636 INFO <general>: ADDON: Dll Destroyed - Zattoo PVR Client
2021-07-22 10:56:35.528 T:653 DEBUG <general>: Thread PeripEventScan 140631045301824 terminating
I'm thankfull for any help ...