What just happened to my Mini Kossel SW?

My Mini Kossel was working just fine.
Today, I decided to change the Z-probes' distance to nozzle by a 10th of a mm, so went straight ahead and did that before I connected to the printer.

It failed to upload (I only changed a number from 5 to six, did not swap a comma with a dot or vice versa).
I did a general troubleshooting, which told me the right Arduino board must be chosen. Hmmm, haven't had to to that before?? So I changed the Arduino board in tools --> board, and while I was at it, I realized I had to change to COM3 in port too.

Now it does upload, but it behaves really strange! Suddenly, in the midst of auto-levelling, it speeds up 3x or so, and starts to miss the print bed among other things.

I let it finish once, to see if maybe it would start printing normal after all, but no such thing; it goes up and down and does strange circles and stuff.

Does anyone know what I might have done?

Thanks,
Edward

Video of strange behaving printer

New discovery; it is only the probing that has issues. I tried fooling around with x, y and y axes manually in pronterface and they all worked the way they should. Also; I am now printing a nice print without autolevelling.

What sort of stupid thing have I done while in Marlin??

It happened to me a lot of times before.

The probe microswitch is not working properly. Either it has a loose connection somewhere or the probe allen key is getting stuck and not hitting the switch reliably. Check your Zmin status using M119