I am just suggesting a possible solution.

I think you suggested that it might be a "splice" in plastic line.

Would it be possible to "snake" inside the line,"plastic", something that would detect metal? i.e. the splice/metal ?

Then remove "snake"  and measure distance above ground  to splice? assuming you have a good line of sight/ memory  of buried line.

Dad would do this with a "wet " spot on known tile line. Dig down in dry ground and run sewer tape to obstruction, then pull out tape, and measure distance(probed tile line) on top.

In this case, it was a raccoon stuck like a cork:>)

Probably better minds at work here, than mine.

Brian