I've just put together my ALAN model cross bike. It's set up as a 9 speed, cassette is 12 - 32. The Sora long cage is new as is the KMC 9 speed chain. The Veloce compact crank and (probably SRAM, lower end) cassette are mildly used. The 9 speed indexed DA bar end shifter is new.
On my trial ride the lowest and highest cogs were smooth but the middle ones 4-6 jumped like crazy. Under load they'd jump/crunch up and down a cog every 1 - 2 seconds. I did run the RD adjuster back and forth with no improvement.
I'll look closely tonight at the cogs but the cassette was perfectly clean and I suspect very lightly used.
I intend to switch to friction mode for a trial run. My Fuji has a wheel with large range cassette (probably 12-30) that I'll also try.
Does anyone have other suggestions on diagnosing this shifting issue?