The session cache was only populated on a fresh username and password
login, so once a session ID was stored in the config every Fs
instance created its own Mega session with its own copy of the
account's node tree. The server side move code relies on all Fs
instances of a user sharing one session, and with separate sessions a
move between two rclone remotes grafted a node from one tree into
another, where the asynchronous event replays of the two sessions
raced and could detach the moved file from the destination directory
so it disappeared from listings.
Cache the session however the login was done. This also stops every
extra Fs instance re-downloading the whole account node tree.
Nick Craig-Wood
74be61735c