How accurate is a TDR (Time Domain Reflectometer) in determining the distance to the location of a cut low voltage cable?
I have a greenlee cs8000 that will work through just about any wall even through conduit, if your electrician has this or a similar tool they can pinpoint a cut or shorted wire.  Time domain meters depend on the information being correct if you thought you had copper wire but it was copper clad Aluminum the distance would be off. Also you need to know the exact path for TDR or you will miss the mark.
Edit; I felt I should expand on my answer because there is some question in my mind if those commenting and or answering have ever used any of these tools
I do not have have a tdr meter but used to use One to test coax on plasma etchers. And is an absolute waste in general construction because it provides a distance based on the wire type and size . I have the other 3 and cable tester.
A toner is not for tracing wires through a wall it is for identifying a conductor in a bundle for example a toner is used in a phone jack in an office building then you go to the switch and can find that wire quickly by running the toner down the punch down panel or in a loose bundle the range is less than 1/2” I have several of these progressive 77 , etch tek (cheap). Data cables Can be live not powered mains Depending on brand
A tracer like the cs8000 can identify a live or dead wire within 1/2” even through metal conduit drywalls and stucco. Any live or dead wire up to 600v direct connect and pickup scanner
tracers for buried wire if you know how to use them can get you within 6” . on wires buried 2-3’ I think mine is a 520 greenlee . Live or dead up to 600v suitcase or direct connect and pickup scanner
Electricians that have and use these tools with competence can identify broken / shorted conductors very close to the open or short.
I think some one mentioned a cable tester (transmitter receiver) you plug in that tests for the correct connections On finished cables they show opens crossed or incorrectly wired connectors I have a couple of these ideal brand is the one I use the most but I don’t remember the model This is the least expensive of the tools mentioned and if you have a mis wire or open at crimp this could be your problem. Anyone doing data should have one of these. Non powered single cable xmit rcv modules on each end  I think the ideal cost ~50$