The error appears in Sync jobs for Read-only agents.
Read-only agents can only download files and pass the unchanged files over to other agents. However, if a file is changed locally on a Read-only agent, it's not propagated to others. Further behavior is controlled by setting "Overwrite any changed files" in the Agent Profile.
If it's set to "Yes", the changed files will be redownloaded from a Read-Write agent.
If the setting is set to "No", the files that changed on a Read-only get invalidated and the agents stops syncing them and the error will show up. Even if these files are updated somehow or deleted on either of Read-Write agent, they won't be synced.
To fix the error set "Overwrite any changed files" to Yes. Folder rescan on read-only agent or the agent restart might be required.
If file invalidation is expected, simply ignore the error message.
Error code: SE_FS_INVALIDATED_FILE