Sorry - forgot to reply to this.
Not sure if Glenn trains, per se. But the population of people like Glenn & myself that spend a considerable time on the trainer in the winter will have a very strong spring, maybe really feel great early summer, then fade after that. Like now.
When you ride the trainer, you are constantly being reminded of what power you're putting out so you have a natural tendency to push yourself. It's also more efficient, since nobody wants to ride 2 hours inside every day. So you get the most out of your hour or hour & a half.
Late spring/early summer rolls around and you're riding more. You have this solid base and you put in solid hours outside. But slowly, you're not pushing ourself as consistently and you start to slide.
Add in the heat and you tend to feel like you're going harder than you are. This July/August especially would have that effect. It feels like you're going hard. And your HR matches this due to heat/dehydration. But facts being facts, you're just not riding with the same power/intensity and your FTP will trend downwards.