I think you’re getting lost in the test results and failing to see all your improvements. FTP is a number to set your training, it is NOT representative of your fitness. It’s about what you can do at and what percentages of your FTP that matters. Also, if you think you test low, simply adjust up your FTP if workouts are too easy. There is no need to retest.
My anecdotal example:
After Traditional Base MV 1, 2, 3, I ramp tested and my FTP was 287 (Jan 15, 2019). I started GBMV and I couldn’t train with this FTP. I overreached the first few workouts then couldn’t even complete workouts by weeks end, so I manually dropped my FTP to 276 (-4%). I could barely get through workouts but I managed and finished GBMV.
March 14th, 2019, at the start of SSB1 (repeating base) I ramp tested again at 287, however I could actually train at this level, granted SSB1 is a bit gentler than Build. April 9th, 2019, started SSB2 and ramp test results were FTP at 293. Ok, small gain but expected since I dropped back to Base. June 15, 2019, starting GBMV (re-build) and I ramp tested at 287… again.
So basically my FTP would say in the past 6 months I have had zero “fitness” gains. Oh, I forgot to mention that my XCO race season started in May 2019. I’ve had 3 races since then and I’ve taken 1st place in each one. My FTP is 10% higher now than it was at the end (peak) of last years race season (September 2018). My workouts at 287 (and the previous 293) were/are completely challenging, but doable. Workouts I dreaded 6 months ago (long sweet spot) I now look forward to. My “fitness” is through the roof and I feel strong and powerful on the trainer and on the trails. I also lost 7 pounds since January. Those are real fitness gains, my FTP is simply a training tool.
That’s because you are! Don’t lose the forest through the trees.