Ramp test results & workout intensity inconsistent

Hi guys, I’m in the middle of low volume build phase. Going in with ftp of 245 (ramp test). I am able to complete most if not all workouts without terrible difficulty.

I just tested again as per the structured plan before I commence the second half of the plan and my ftp has gone down to 240.

Do you guys have a similar experience?

Should I stick to 245 or 240 for the second half of my build phase? I thought of sticking to 245 cos the first half has been relatively okay, although I did finish it with a lot of fatigue.