Ok I had just typed up a long post, but the summary was yes, it is all neural.
First though I'd liketo know,
1. Why did you deload?
2. How much did you "feel" like squatting during those first 7 weeks, versus the other 4 weeks when you lost strength?
After one week of deloading, you said 405 felt heavy. From my own experience, i think this is because the volume was WAY too low. Keeping voume higher will keep the motor pattern for squatting intact. That's one fo the benefits of lifting for higher reps, versus performing singles and soubles all the time, your body becomes used to this movement, and you feel like doing it more.
The past two months with deadlifting, I had the same problem, I deloaded and got weaker. I conclude it's from low volume heavy work, btu also starting bounds and sprints, which change the neural drive. So right now, I chenged my program entirely to accomodate this, because I can't make significant gains in deadlifting while bounding for isntance.
I'm wondering how much you "felt" like squatting because that can tell you how recovered you are in some circumstances. I don't think you were lacking in recovery during the last four wees, In fact I think you were taking too much time off, and your body was not used to this.