In its storied 51-year history, Fleetwood Mac has had more than its share of issues — there was the frontman who suffered from schizophrenia, intra-band romances and breakups, personnel exits and returns, and, this year, the inexplicable firing of its guitarist of 40-some years.

So maybe it's fitting that Cantus, the acclaimed Twin Cities all-male a cappella classical octet, had its share of issues doing its annual pop covers concert, this time featuring Fleetwood Mac.

The issues on Friday's opening night (of five concerts)?

First, the air conditioning at Cowles Center in downtown Minneapolis wasn't working. Ugh.

Secondly, Sam Green, one of two bass singers in the group, was out with strep throat and pneumonia.

But as Chris Foss, the other bass singer, said early in the night, after explaining that a wheel literally fell off his car in the afternoon: "Nothing is going to stop this show. If the power goes out, we'll do it acoustic a cappella in the dark."

Well, the power did go out, on Zachary Colby's microphone in mid-solo during one number. A stage hand awkwardly scurried onstage to hand him a new microphone with working batteries.

That was the least of Cantus' problems. The tenor-heavy ensemble missed Green's bottom sound, especially since bass vocalist Foss was often preoccupied with playing guitar instead of singing. The blend and balance seemed shortchanged at times.

Similarly significant is Cantus hasn't found an imaginative approach to its interpretations of Fleetwood Mac's familiar songs. Too many of the 13 Mac numbers — including a re-creation of the classic 1976 "Rumours" album — were faithful to the recorded versions.

Is Cantus trying to be a cover band or a cappella interpreters of pop music like, say, Pentatonix?

Cantus can't compete with popular barroom attractions that dutifully recreate the sounds of well-known songs. The three fine musicians backing Cantus are hired pros reading sheet music. Guitarist Foss, the fourth instrumentalist, is capable but can't fully concentrate on his vocals or guitar.

So why doesn't Cantus stick to what they're known for — a cappella singing? Even just doing rote readings of the well-known songs like "You Make Loving Fun" with eight-part harmony and no instruments would be appealing.

As it was, there were still a few moments of musical inspiration. On "Never Going Back Again," there was an attractive playfulness to the ping-ponging "dum dums," punctuated by Colby's bird-like chirping. And "Songbird" was beautiful in its a cappella simplicity, with close choral harmonies and Paul Scholtz's high tenor soaring with the best lead vocal of the program.

As for the eight non-Fleetwood Mac pieces, there was one stand-out: Cyndi Lauper's "Time After Time." Cantus transformed the emotional ballad into a twangy country tune before shifting mid-song into a peppy bluegrass hoedown. That's Cantus at its best in the pop realm.

Another winner was the encore of Celine Dion's "It's All Coming Back to Me Now," which was campy and sincere at the same time thanks to baritone David Geist's lead vocal turn.

But there were too many missed opportunities. Why didn't they camp up Destiny's Child's "Bill Bills Bills"? Why didn't they enliven Pentatonix's Daft Punk medley? Why weren't there any wow moments like last year's "Bohemian Rhapsody" during a Beatles' "Sgt. Pepper's" show or 2016's "Thrift Shop" during a Beach Boys' "Pet Sounds" show?

In this pop covers context, Cantus, at best, issues or not, offers pop music for a non-pop audience.