Interesting issue for the community. Tried to use the z touch plate this morning and it didn't work. It had worked fine yesterday. Long story short, I traced it down to the router. The probe had good continuity between it and the frame. Then I checked the continuity between bit and frame and got nothing. Router frame (Bosch 1617) continuity to Axiom mount is good. Removed the router and there is no continuity between router collet/spindle and the router frame. That's why the touch plate didn't work.
I have another 1617 router and I checked it for continuity and it is just fine. Swapped routers and I'm back in business. Still very strange issue. Why would this happen? Does it mean that I'm getting read to have to rebuild that router? Router works just fine like it is, just doesn't ground the bit to the frame any more.
I have not seen this issue reported anywhere I thought I would post it to this forum in hopes that it could save someone else some trouble at some point.
You probably could have "fixed this" (at least temporarily) by manually spinning the router shaft. It may be that it just happened to stop in "just the right spot" where the brushes weren't contacting the pole of the armature due to dust or crud or wear. This microvolt continuity would be the "first thing to go" in that situation (since the higher current while the router is energized is still "bridging that gap"). Pull the brushes out of the router and examine them. While they're out, blow out the inside of the router with compressed air. If you need to replace the brushes, they're only about $10-$16. As long as the bearings are good and you haven't cooked the windings on the motor (due to long run times and heat buildup), you shouldn't need to consider replacing the router.