You called? 
@WOB you’re getting a bunch of great advice on here! A few thoughts.
FTP is a theoretical number. All FTP test protocols are just a way of benchmarking YOUR progress, and your progress is all that matters (not the absolute # or how it compares to anyone else). As Chad said on Beers With Chad, it’s just an assessment – and a temporary one at that. It’s just a snapshot of one moment in time. AND it does not take away from all of the benefits you’ve reaped from all of the work you’ve done! You’re moving your body consistently with the time that you have. That’s awesome! Give yourself due credit. So - with that perspective in mind…
I like to look at things like this with enthusiastic curiosity, like I’m solving a puzzle. First - you’re being consistent with your test protocol, so that’s probably giving you a good picture of your progress. (People often see different absolute results using different tests, but using the same test should give you decent benchmarks, regardless.) Second, you’ve been very consistent with your workouts, and that’s usually the prime culprit when folks don’t see FTP increases. So, we can likely eliminate those 2 factors.
I echo the suggestions of others to try fueling your workouts. Fasted riding, especially in Sweet Spot, is not only difficult, but also impairs power output at intensities > Tempo (so Sweet Spot, Threshold, VO2, anaerobic, and sprint). If you fuel and maintain higher power output as a result, workout after workout, you’re more likely to see more gains in terms of absolute power. Although your workouts are 60 minutes, they are high intensity work (if you’re doing Sweet Spot). The amount of fuel you need correlates more with intensity than with duration. 60 minutes of active recovery is fine to do fasted, but 60 minutes of Sweet Spot or VO2 work is a totally different story.
Another factor is your training history and your individual physiology. My body LOVES steady state work. I could do Sweet Spot all day long, but training in Sweet Spot increases my FTP less than progressing my Threshold and VO2 zones. It’s just how my individual physiology works. So, I see some gains in SSB, but much bigger gains when I get to Build. (BUT that’s with the caveat that I fueled my SSB blocks!)
AFTER you try fueling, you may want to try swapping in a 60 min short-burst VO2 workout like Taylor -2 or Gendarme for those longer rides, instead of swapping in a 60-min Sweet Spot workout. This will get you closer to the target TSS for those days and will give you an idea of whether your body responds well to some higher-end work. (For what it’s worth, the Build Phase will include plenty of this!) I don’t think increasing your volume is the only way to make FTP gains, especially given your time constraints. I’d try this first and give it a full block with appropriate recovery (and definitely be sure to fuel these).
Lastly, I do think it’s worth considering whether the intensity level is correct. I am naturally inclined toward Sweet Spot work, but even for me, it never feels easy. I do think (as stated) that using the same test protocol will give you an accurate picture of your progress; however, each test type does yield a different absolute value (again FTP is a theoretical number, so it’s impossible to measure directly). TR workouts are specifically designed to be used with the Ramp Test, so testing with the Ramp Test might give you a more appropriate number in terms of calibrating the intensity of the workouts correctly for you. I know some folks like to use the protocol that gives them the highest number, but that isn’t the point of the test. It’s just a benchmark to understand what your body needs right now to progress.
If you have time in your training plan, I’d suggest trying SSB I again. Start with the Ramp Test, and mentally use this as your Zero Point. No comparing to anyone else, or anything before that. This time, fuel all of your workouts. Try that for a couple of weeks and see how you feel. If you’re adjusting well and feeling good with that, then start swapping in a 60-min VO2 short-burst instead of 60-min Sweet Spot for the longer rides and see how that goes for a couple of weeks. (Fuel the VO2 workouts too of course!)
You’re doing great work already, and you’re learning a ton. The consistency you’ve shown is impressive, and for most folks, that’s the hardest part. You’re not seeing the outcomes you want (yet), but that doesn’t mean you aren’t getting a lot of things right. Ease up on the judgement, and lean into curiosity. What a cool puzzle this will be! Just think of how much you’ll learn about what your body needs and responds to best! Keep us posted please!
