Electrical – 2 breakers powering 1 set of outlets

this is my first time posting a question to a forum like this.

Electrician added a breaker and ran a line to an outlet that had power from a different circuit but had a short in it that could not be located. Is this safe?

Here is the whole story…

Plugged a vacuum in and it started and then went off right away. Also, lost power to 2 other outlets and lights in another room and hallway. On the same breaker there is the bathroom plug with GFI, light fixture and fan all working as expected including the GFI. The breaker was not tripped but I did flip all the breakers off and on a couple times to be sure. I reset all GFI in the house. I removed and replaced the original outlet that caused outage, then replaced another and before replacing the 3rd I used a non-contact meter to see that the wire to the outlet was not getting power. At this point I decided it was time to call an electrician.

I found the electrician on Angies list – they had an A rating and many positive reviews. They gave me the pricing and told me they start with an hour and that is usually enough time to find and fix the problem but if not that they would be able to give me an estimate for the work required, time and price. They came out the next day, the electrician and his apprentice. They looked at all the outlets with no contact meter, pulled out a few of the plugs on the circuit for this breaker to check for loose connections, took a couple of the lights that were out down and checked connections, traced lines in the crawlspace and attic and were unable to find the break in the connection.

After an hour and a half they had not found the cause of the outage but had found a melted connection on the GFI and had removed it. They told me that they could stop there and not charge me for the time – only the GFI replacement or they could keep going but would need to charge me the hourly rate. I said keep going. They looked for another 2 hours in the attic and crawlspace and were unable to find the break in connection. Said there was a line running down into a wall that didn't seem to have any outlets near it and that maybe there was a hidden junction box (even though I said I don't remember one from the complete gut down to studs that I performed 3 years earlier).

At this point the electrician said that he could not find the problem and that the only thing he could do was to put in a new breaker and run a new line to the original outlet (which only had one hot one neutral running to it). Since there were unable to find the break they were not able to disconnect the line that should have been powering it. But when I do find it the hidden junction box or loose connection (I told them I was going to be remodeling the kitchen in the next month) to cap it off. Basically they added another breaker to feed power to the outlets that lost power.

He told me 4 times before leaving to make sure that the smoke alarms worked.

After some more research I think that what he did is very unsafe so I turned the new breaker off. Is what he did safe? Can I leave it like this?

After they left I realized they never checked the bathroom light fixture – and that it is about where they said there was a line going down the wall and I had replaced a lightbulb around the same time the issue started (although I am not sure exactly when the power went out only noticed after vacuum incident). I am going to check it out the bathroom light fixture tomorrow but if that is not the problem what should I do. And if it is the problem should I cap off the extra wires here or should I fix connection and then disconnect the new line added?