My fitness does this a lot, so I feel your pain. For me training is much different than racing, even with interval work, I often find the actual races to be different/harder because you don't get the same level of breaks that you do in training. If you are not training and racing with a power meter, you really can't compare the two, so it is hard to know what is going right and what is not.

In general train with a higher cadence than you think is comfortable and with less resting time a few times a week. To me this makes it more like a race and is something that might help you. 8 to 10 hours is enough to keep up with the 2/3 level races if you train right and have been there before. For me that means intervals up to 3 times a week, for you maybe something else, but I would start to focus on some mixtures of intervals along with some varied cadences to help simulate races.

I do one FTP session per week, one VO2 Max session and one sprint session total of 5 hours. The I add in one endurance session at 2 to 4 hours at mostly below FTP/easy breathing, to me these are the 4 workouts not to miss each week, the other 2 or 3 times I ride are JRA and meant to spin out the bad stuff, top off my fitness or make a single effort depending on how I feel. I sub in races for any of the days depending on where I am with my schedule.

Also make sure you are not working too much in the races, a lot of time spent with your nose in the wind could be your issue as well. Stay back and be lazy if you feel you are not finishing the races strongly enough - or go harder and build up some fitness, but don't be overly worried about things until you feel your fitness is back to where it was in the past.