Well, I no longer do specialty phase, I tried it again in 2020 and was too much. So, I’ve been focusing on base and time in zone so a lot of sweet spot working to 90 minutes in SS. Then after 3-4 months of that I’m doing a lighter build with limited Vo2 and only 2 key workouts a week. I’ve had good results at 3 crits and a few fast 50-70 mile group road rides. My goal is not to peak for an A race but to be strong from June through the fall so I need to be somewhat fast for 5 months so stick to base type workouts with some build workouts sprinkled in to be fast when needed.
Two things stand out - you didn’t list the volume of the specialty plan, but take a look at the TSS compared to your previous plans. If you are outrunning your current fitness by way of load, that could be presenting some problems. You might need to replace a session with endurance until your fitness catches up.
If TSS is roughly aligned, I would be willing to bet your power curve is weak on the high end. The benchmarking for Zone 5 plus is still built around population averages and 140% intervals for example might be an achievable challenge for some and impossible for others. This is a shining example of a great use case for Adaptive Training. I suspect the levels built into the canned specialty plan are beyond your levels. There are workouts that will accomplish the intention at a lower intensity either by volume or interval intensity that will allow you to progress toward your goals. Striped +1 is no joke, it is a 7.6, failing that workout is a high probability for a LOT of folks on this platform. Your level might be a respectable 5 or 6 and those workouts are just too much of an overreach. If you’re not on AT, take a look at the workout levels as compared to what you were being served up in build that you were achieving and you might have to dig around the variants/alternates for a better match.
I think your conundrum is more common than you think. 