Failed to route the following signal

Long synthesis times and a no-route are technically different. Once it's through synthesis, it's a structuryal netlist that gets passed to the fitter. That being said, a day long synthesis is REALLY long. I've never seen anything close to that. Is 99K LEs about what you'd expect? Perhaps you're running on a slow machine?

THe times I've seen synthesis run off into the weeds is when designs are purely abstract, and the user expects things to get synthesized out. For example, I saw one that was only 50K LUTs, but when I started synthesized sub-modules by themselves(so reductions wouldn't occur) small hierarchies blew up to hundreds of thousands of LUTs. So basically synthesis was creating over a million LUTs and then finding reductions to bring it down to ~50K. That is very uncommon, and not what synthesis is really designed to do.