A friend who’s an episodic TV director once told me — when I expressed affection for “Profiler” and its star Ally Walker — that it had a reputation as a “troubled show.” So too have I heard from people that Donald Bellisario, creator and majordomo of “NCIS,” is, to put it blandly, a wee bit erratic and tempestuous.

Sure enough, the very next season of “Profiler,” Walker was out and replaced with Jamie Luner, an up-from-bad-cable casting call actress of no distinction whatsoever. Walker has yet to reclaim a major career.

And Bellisario, by some reports, was a seasonlong target by “NCIS” star Mark Harmon to have him thrown under a bus.

Now that I’ve been apprised of the industrial “troubled” diagnosis, I’ve begun to see its symptoms on the air — the sudden moment in “NCIS” when Harmon’s character supposedly quit, grew a beard and went to Mexico (a backstage star/showrunner face off?), the sudden disappearance forever of Lola Glaudini from the cast of “Criminal Minds” to be replaced by Paget Brewster, an interesting and lovely actress but one whose dramatic affect is several shades lighter than Glaudini’s.

Patinkin, if you remember “Criminal Minds’ ” beginnings, was a tormented FBI profiler who, it was hinted, was himself a wee bit nuts, in a genteel, high-functioning way.

All that went by the wayside as the show proceeded. With every new episode, Patinkin’s character seemed to lose personality. At the same time, young characters developed drug problems and suddenly juicy pasts while Patinkin’s character turned into a totem pole muttering sagacious lines, and standard cop things and then exiting stage left while everyone else did the emotional heavy lifting.

For weeks on end, William Petersen had more emotional depth and quirks on “CSI” than Patinkin on “Criminal Minds.” (Petersen, according to TV Guide, is also paid $500,000 an episode.) That can’t have been fun, especially for a tempestuous, show-stopping Broadway singer like Patinkin who’d already taken a cab from one TV show (“Chicago Hope”) and who was clearly only doing prime-time TV to pay for the kids’ tuitions and better real estate holdings.

And too, Patinkin has had publicized health problems in the last 15 years. (Eye surgery.)

I have to have been, then, one of the least surprised critics in the world to learn that Patinkin had done a Johnny Paycheck (whose great country hit, you’ll remember was “Take This Job and Shove It.”).

The trouble is this: I watch “Criminal Minds,” a kind of pitilessly pedagogical collective version of a nicely eccentric show like “Profiler.” I don’t know how they’re going to replace Patinkin’s squirrelly genius character but I’m, at best, dubious. Jamie Luner, after all, is probably still looking for work.

A show with no differences, and no creativity either, isn’t such a great idea