I've had the same issues as you where the plastic doesn't stick well to the print bed at the corners. Printing at 0.1mm resolution solved the problem for me. 0.2mm and above just won't work on large prints on my Da Vinci 1.0. In cases where I had to do 0.2mm resolution (because the  slicer gave errors when I used 0.1mm on more complex parts...), I put duck tape over the print bed and applied glue over it. The ABS stuck very well to the duck tape. The only thing to remember is not to remove the duck tape while the print bed is still hot because it's sticky side is going to make a mess. I hope this works for you

I have a camera watching mine print and the printer is plugged into an wifi controlled plug, so that I can monitor and shut off the print remotely. Considering how long prints can take and how often a complex print will fail it seemed like the best solution.

If I was to make a guess...

Connector came "loose enough" where it was at to lose power and nozzle became trapped against print when it cooled enough that it couldn't break free of the ABS. If the extruder was running at full temp, you'd have gotten far more than a "small brown" circle on your print. The ABS would be so burned near the extruder that it would be black just like the stuff is that gets stuck to the extruder that you scrape it off with the brush.

Another even more likely possibility is that you lost power for a minute or more. That would have given you that same effect but wouldn't have been the printers fault. On the DaVinci when power was restored it would try to park the head but wouldn't be able to. Considering the "light was out" this would make sense depending on your firmware version. On my version the light stays on during the entire print including after printing stops if you don't press "ok" after it's cooled down, so if the light is ever off that means I lost power during the print (version G). On other versions the light follows different rules.

Here is my situation.

Printed the 3D demo keychain no problem.  Printed another object that took 2 hours without much issue (minor warping and didnt stay tacked down in one corner).

Attempted a larger print, 8 hour print.  2 of the corners failed to stay tacked down (glue issue?) I was using rafting and supports.  I'm using the most recent firmware and software released.  The extrude got "stuck" 53% complete at last build attempt.  I was away and returned to a quiet machine.  On pressing ok(the lights where off) to see whats happening the screen lite up with project print canceling... the extruder was stuck to the top back right of the print in the plastic...it was trying to move about and was shacking the plateform badly.  It took me only a second to realize shit hit the fan, I reached around back to shut the power down.

I freed the stuck extruder and cranked the platform down a bit by hand to make sure it would clear.  The device returned to its starting position.  The extruder warms up to its seemingly normal range of operation tempature, and the machine appears to be working correctly...

The point at which it became "stuck" had minor brown burning in a small cricle but wasnt built up enough to stop operations in my opinion.  Its as if the extruder stayed in one place to long and lost heat and became stuck...

Off hand I was using stock ware software, high density, .3 layering, normal speed.

I'll include pictures of the failure point when I get home (currently using mobile device to post).

Should I recalibrate?  What do you think happened? How can I prevent wasting plastic, time, and builds in later prints?

I'll be looking into slic3r software later tonight with a update.

Sorry for typos and lack of photo support for the problem I'll update when I get home.