The phrase "nice groove" means that something, like a song or rhythm, has a smooth and pleasing flow that makes you want to move or dance to it. Full definition
When she finally hopped in after I miserably failed to complete the level, things got more manageable and extremely enjoyable: we focused on one half of the map and got into a pretty nice groove. (monstervine.com)
You may be in a nice groove, then all of a sudden, things change again. (verywellfamily.com)
I love when we get back into a nice groove with set schedules and this week has been easing us back into it for the rest of the year until SUMMER! (adashofpretty.com)