I was talking about A/V streaming buffer, because you didn't mentioned a specific buffer. Kodi's default setting includes Samba caching into RAM. Maybe you have to increase the "memorysize" parameter to keep the whole Samba cache in RAM.
I was just asking about any buffer that might need flushing to an external USB drive. Something causes LibreElec/Kodi/RPi4 to corrupt an attached 6TB HDD. This does not happen with the RPi3 and its older s/w. What I need is to identify why so that I have a chance of stopping it happening and I can switch over to the RPi4.
So back to the question - does LibreElec/Kodi/RPi4 flush any outstanding buffers to an external USB HDD before rebooting or powering off?