Are you waiting to clear cookies until AFTER your first SSI credits? That's the only thing I can think of. You can certainly take both the SSI and SSI2 on the same day. I usually do the first one, wait til it credits, then clear cookies and usually will try for the SSI2 later in the day then depending on how much time I have...
Other than that, sounds like you're doing everything right, hope you start getting them soon!