Thanks again, for all the info and the help. I'm new to debuggers and I couldn't do this without help.
I forgot to try rolling back the firmware, but I got around to it today. The probe I'm using is v2.3b, which got supported in 1.8.0. I didn't realize it until after I flashed 1.7.1, which caused it to not respond when attached to the board. The latest stables are 1.8.0 and 1.8.2.
I've tried a few different firmware versions. I made a fresh project with an unmodified board.txt when testing these. All loaded with DFU-util:
1.7.1 - Doesn't work
1.8.0/1.8.2 - Fails in VS, iffy in CMD. They behave the same, and I've attached the output from "Attach to process". The error is different than the one I posted when I was on 1.9.0rc0. I want to add that, when interfacing with it via CLI, the probe had a 50/50 chance as to whether or not it was able to find the board with "monitor swdp_scan", or just outright freeze at "Target voltage 3.3v".
1.9.0-rc1 - Fails in VS, almost working in CMD. Similar result to 1.9.0-rc0. Output file attached. This firmware works well in the command line, more of the functions/commands work, it's very consistent, the only problem I'm having over CLI is I cannot add breakpoints. When I try to add a breakpoint to setup/main/loop I get this error, even after I deleted all breakpoints (and it shows no breakpoints):
"Warning:
Cannot insert hardware breakpoint [number].
Could not insert hardware breakpoints:
You may have requested too many hardware breakpoints/watchpoints."
I couldn't even get that far in 1.9.0rc0, for what it's worth. I'd like the convenience of debugging in VS if possible, but for the project I'm working on right now, just getting it set up in CLI would be huge.
I bought my board off of Adafruit's website. Here's the store link I used:
https://www.adafruit.com/product/3839 I'm going to test my ribbon cable connections later today, and I think I can get access to another PC, to see if it's something with my computer.