First off - Another great telling, Cormanus, and nice hat.
"I can’t begin to say how annoying that was. I usually wing it, but this time I’d done an enormous amount of work to program a route into my Sygic app. All for nothing." -- I think you and I are in the minority group that actually enjoys the planning of a ride. I view a well-planned route as something akin to a gift I'm giving to those riding behind me. If I'm planning a solo route, I usually am doing so to be sure I hit a certain road at a certain intersection or a certain place at a certain time and I've headed out on rides with those goals but no set route and, as often as not, miss that road or that restaurant that I had in my head.
Don't get me wrong, I appreciate the "You just go" attitude of the Johnny Strabler and there are many times when I just go, but I get frustrated with the in-route forced change; a) because I'm not big on change to begin with, b) I feel like I dropped the "gift" on the way to the party, and c) usually the change is caused by some other unpleasant circumstance like rain, mechanical issues, construction, or illness any one of which just adds to the frustration.
May your routes go as planned frequently and when they do not, may the unplanned route unveil something new and wonderful...and dry.