Flow node instance with id xxxxx not found - Appears randomly

I have make a java application that start process when a file apear in a specific folder.
When we valid the 'human task', the process start a sub process to upload current file with some metadatas in a GED.
Sometimes, the subprocess can't be found, and we don't know why.

You can find BOS files and the log file of this error in attachment.

Regards,