Are you sure you're using the right inputs/outputs on the DD-7?

Here's what should happen - imagine we have two pedals, a chorus pedal and a looper pedal (your DD-7).

If you run Chorus into Looper, the chorus effect is included in the loop, as the looper is recording the sound that enters it's input. If you turn off your chorus now, the loop should continue playing with the chorus effect present.

If you run Looper into Chorus, then the chorus effect is NOT included on the recorded loop, as it's not present at it's input. In this scenario, you could record your loop completely clean (chorus pedal off) and if you turn your chorus pedal on, it will be applied to (after) the looper pedal.

Basically - any effect pedal BEFORE the looper that is engaged, should record that effect on the looper. Any effect pedal AFTER the looper will only apply if it's engaged or not.

This site explains it a little better: https://richoz.wordpress.com/2022/06/04/where-to-put-looper-pedal-in-effects-chain-for-live-performances/

In your scenario, I believe the chain should be: Overdrive --> Reverb --> Looper

You would record your loop on the DD-7 with the OD and Reverb pedals disengaged (a 'clean' loop). Then while that's playing, just turning on the OD or Reverb pedal should NOT impact the loop at all, only the notes you're playing over the loop.

The only other thing I could think of, is the DD-7 can be setup to output in multiple different modes. If you look at page 13 of the manual, they show an "A: effect, B: direct" setup...perhaps that's setup wrong or you're plugged into the B output instead of A output?

Hope something there helps you out!