Resilio Connect Agents rely on modification timestamp (mtime) to know whether a file has changed and whether it needs to be delivered to other Agents. After receiving the files, Agents will try and update the file's mtime to match that on the source Agent. This basically means that Agent will perform "change attribute" operation on file.
Sometimes this may fail as the process may not be allowed to change files' attributes and the Agent gives the error. This is especially the case for mounted network shares.
The fix would be to allow the user who runs Agent's process to change files' attributes.
On windows it can be done from Advanced security settings on files and folders
On linux it's required that only the owner of file can change files' modified timestamp to some specific (non-current) value. By default, newly delivered files are owned by the user who runs the process, while this may be not the case of pre-seeded files. Change the owner of those files and restart the agent.
A workaround for all platforms is to instruct Agent not to even try to update mtime, but rather keep it in database. Add the following parameter to the Agents profile and restart the Agent ignore_mtime_assign_errors:true. With this Agent will keep the current timestamp as 'modified' on the file, but will store the proper mtime in database.