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For proper video processing, the GPU memory needs to be set to at least 320 MB on the RPi4. If that hasn't been set yet, please do so.
Also, a kodi.log file could be informative as to which processes are possibly running in the background.
Please provide a full debug log.How to post a log (wiki)1. Enable debugging in Settings>System Settings>Logging2. Restart Kodi3. Replicate the problem4. Generate a log URL (do not post/upload logs to the forum)
use "Settings > LibreELEC > System > Paste system logs" or run "pastekodi" over SSH, then post the URL link
use "Settings > LibreELEC > System > Paste system logs" or run "pastekodi" over SSH, then post the URL link