Some years ago i went through a similar patch where i struggled to do 100k rides! I never worked out the cause but eventually was back to my old self and enjoying rides up to 300k as this ive found is my limit in terms of enjoyment versus suffering! All the best!
A 600 sounds like a heck of challenge as a solo DIY Richard (as well as just plain too long for me, full stop!). The mental game is as hard as the physical ride at the longer distances on your own. I'd say congratulations on getting as far as you did, recognising when it is wise to stop and having the guts to make the call. Chapeau! BTW - what are the earphones you use?
If I've learned anything from cycling it's that regardless of the route you choose, you'll always have an uphill, literally or metaphorically. Be safe and have fun my friend!
Attempting 600km DIY rides is audacious - calendar rides of that length are incredibly tough even with the support from controls, other riders etc. Did you struggle at the same time on both rides? - if yes then maybe changing the time you start might be worth considering? Getting the night riding done with the inevitable slump around dawn early in the ride might possibly help? Or possibly try to plan a short sleep stop?
It's tough doing the long rides DIY - they can be pretty boring, and there are always down times where you have to lift yourself up. It's a bit easier on calendar events because kindred spirits can give you a boost when you need it, and vice versa. I think it takes maximum mojo to do the very long rides DIY - so I wouldn't see it as a mojo failure: just a temporary reduction in maximum mojo. Good luck on the next one - a hyper SR is quite something.
I'm no expert (my longest ride is only 200K) but is it worth trying a different route next attempt? I'm thinking this route has too many 'demons' now ? Just a thought
