A couple of thoughts come to mind:
- Maybe it's the driving, not the engine. IOW, it sounds like you're accustomed to gaps opening up and you rely on your FTP and 5 minute power to roll them closed again but your team mates with less sustainable power at their disposal are doing a better job of 'gap management' or that learned ability to see the attacks coming wind up a gear quickly to respond and are following wheels while you might be dieseling your way across no man's land. You can probably get away with that on many group rides where the competitive bursts are shorter lived and less frequent but throw a couple of dozen fit and aggressive riders at similar levels into the mix and each gap that isn't closed immediately is one more match you're burning while others are following wheels.
- In a way, your sustainable power may be leading you into this trap as you generally know you can roll folks down but it doesn't work as well as you face more comparable competition and likely won't work so well if you upgrade.
- From a physiology standpoint you might want to develop your ability to quickly recruit muscle groups on demand with workouts like Bill Black's HOP work that both teaches you to accelerate quickly and forces you to recover at relatively high intensity. You can create many variations on micro-interval work but I recommend folks start with some basic 'Tempo with a twist' where you go out ramp up to mid to high Tempo and do a seated 10 to 15 second burst every two minutes before settling right back into your Tempo pace. The goal on each burst is a dynamic and very rapid acceleration using leg speed, not brute force to whip your cranks up and wind them like crazy in the saddle before settling back to Tempo for recovery. There aren't really power goals for those bursts just focus on immediate acceleration and then go home and see what you actually did hit for the early and late bursts. Sustain the overall efforts just like you might a pure Threshold effort so maybe 2x20 or 2x30 or 1x60. Those bursts will really drive up the NP so these can be quite hard. If they're not hard enough you can do the bursts more frequently or raise the base Tempo intensity a bit. I'd hold off on stretching the 'on' periods as from what you describe rapid acceleration sounds more useful than lactate tolerance right now but that's another very useful flavor of these.
- If you race many crits, especially regular training crits then play with them to work on rapidly responding to surges and getting up to speed immediately out of every corner. Perhaps set a goal of riding the whole crit a gear or two or even more lower than usual and perhaps trying as hard as you can to never jump out of the saddle to respond or finish a corner.
- If you suspect it's more on the driving part, really pay attention to what's happening up front regardless of how deep you're riding in the field and also pay attention to any movement up the sides as early warnings of upcoming surges. Try riding a cog or two lower than usual when the group is rolling moderate speeds and attacks are imminent and only upshift to bigger gearing after whipping your gears up to speed and grabbing a wheel. I love grinding a big gear in a TT or in an L4 training effort or when off the front solo or with a small break but in the field I try to ride a much lighter gear unless we're going flat out and I really need all the gearing or we're going so fast that further attacks are unlikely at those speeds. It's amazing how many folks (and I'm not suggesting you do this) wait till the wheel in front of them starts to accelerate and then jump up in a big gear to grind up to speed instead of looking forward anticipating the surge, riding a bit of calculated but hopefully safe overlap and whipping smaller gears up to speed before the ranks ahead have started to respond. Do it well and it's like the free ride as you just slip in behind those guys as they ramp up to speed. In those cases where they're too slow on the uptake you use that early acceleration to blast right across the gaps they open up. Sometimes that relatively easy in the saddle acceleration takes you right up front at speed just as the leaders decide not to follow through with their surge, when that happens you just roll that easy speed to get a free gap with no huge effort and put your TT and slowtwitch strengths to use without first having to burn a big match to open the initial gap.
Yeah, I'm making tons of assumptions here and maybe you already do all these things really well but that's what came to mind after reading your post.
Good luck,
-Dave