Trying to figure out what wonky USB audio settings make Renoise unhap

I bought a Behringer UMC404HC USB audio interface to have more simultaneous recording inputs.

I mainly do recording in Reaper, and had everything working fine, until I (I believe) did something to misconfigure theUMC404HC.

When trying to use it in Reaper, the transport doesn’t move, though the “play” indicator is green.

In Renoise, a song will play, but haltingly, indiscretechunks, not smoothly as it should.

I thought I figured out the issues: I was telling Reaper to use 2 outputs (since I really only wanted basic stereo), not the 4 available. But now, even after making that change, I get the same broken behavior in Reaper, and that weird chunky play-back in Renoise.

This is not a Renoise issue, but I’m hoping someone else has run into this and has some insight.

I’m going to put aside some time to work this out (and take notes), but perhaps someone has some information to point me in the right direction.

(As I write this I realize I need to locate any and all log files and see if they hold any useful data.)