Some background - Spent 4 weeks in France for mix of vacation/work. It was epic. Shipped my bike in the Ninja case - worked out great - happy to share any advice with others thinking about such a trip.
Most kJ I’ve ever done in a month by about 20%, climbed almost 75k feet, etc. Typically on the HC climbs, I’d target 75-85% average - sometimes lower if doing two in a day or heat cracked me; sometimes higher if I was a bit more recovered or it was only cat 1 climb.
While there, they also experienced record heatwave last two weeks. This convoluted a lot of things as everything was harder. By the end of the trip, my HR was regularly running 10 BPM higher for same power output, I struggled to get my HR up over threshold - sometimes struggled to even hit threshold. Heat didn’t help but also seemed like signs of fatigue. Came home and rested 9 days - some hard outdoor work but off bike.
According to Golden Cheetah, I did more time in L4 (90-100%) by more than 2x what I had ever done in any other month - but I think a lot of this L4 time was oscillating just over/under L3/L4. Basically, a ridiculously big load (for me) of mid-high tempo work - which many say is a no-man’s-land for training - and a lot of coasting down hills 
(PS - carbon rim brakes are no fun in the Alps!)
First group ride back felt great - a lot of 2019 and a few all time ~5 min power PRs. Ramp test today showed I was down 7W on FTP. This isn’t too surprising… I rode no structured intervals for past couple months, and rarely pushed myself over FTP while in the Alps, as I was typically aiming for longer rides.
With all that - I’m slightly uncertain what approach to take now. Finished most of sustained power build before France.
The common advice I see here is go back to SS base - maybe SS base 2 - and let group rides cover the upper end. I’m thinking about that… but again, that means no structured intensity.
And I suspect the biggest deficiency for me in past month that may be holding back FTP was a drop in structured time at L5/6 - which would suggest something like repeating build - and calling that month of climbing my redo of SS base. I don’t see that path advised nearly as often.
I have a 75 mile event in just over 3 weeks as well so will do a light taper for that. Not a crit/cat racer - prefer gran fondos and longer riding. Goals are to build FTP (which I keep stagnating on) and better endurance at ~70% of FTP (which has improved in past year)
Thoughts?