Hi @bvelte, as mentioned before n8n isn’t the ideal tool for syncing large amounts of binary data between two sources. A stuck workflow could suggest a memory problem, especially if there are additional error messages.
So you might want to consider a different tool for this job. In the past I’ve suggested rclone for this and I think it might also handle your case quite well. It can connect to both FTP and Nextcloud (via WebDAV) and could be controlled by n8n using the Execute Command (if rclone is available on the n8n server/in the n8n docker container) or SSH nodes.
There’s also the experimental variable N8N_DEFAULT_BINARY_DATA_MODE=filesystem which you can set on the latest n8n versions to prevent n8n from loading binary data into memory and use the filesystem instead. This would, however, not change the behaviour of the merge node. Could you share the data returned by both nodes connecting to your Merge node’s inputs when you workflow stops and confirm which (if any) errors you are seeing?