If it's done that after 30 miles, then almost definitely clearances have not been correct, spun shells are normally due to wear/picking up or oil break down.
If someone else has done the work it's 100% down to them, shells should have been sized/supplied correctly when crank was ground.
What thrust did they set it to, should be around 5 thou ideally, the newer all steel thrusts from Glyco(federal mogul) etc are ok but the older original ones are better, I've re-used my 200,000 mile old thrusts, and still well within limits.
tabetha