I also experience the default behaviour as problematic. The way this is suppose to be engineered is:

1. You save the max bitrate footage to sd card, that way you are guaranteed to have no network latency problems.
2. Directly after the file is written and the motion stops, you upload said file to the ftp server, this can experience connect retries (no problem), this can experience slowness (no problem), and so on.
3. You tell the user the FTP feature is NOT available without sd card. Which is completely reasonable. Streaming to a ftp location is asking for problems.

edit: I have a 510wa by the way. Which I would love to connect to wired, but just can’t due to its location. So the stability of the sd card is even more important. The wifi is fast but nothing beats local storage, except for the fact that I need to have those files in a secure ftp location as soon as possible.