So this happened the other day. Apparently I did it backward and lost a multi-level. I thought if I hit skip level it would abandon the game, so I did multi-level, clicked on the same level, then hit skip level, thinking it would take me to the next level. So that's not how it works, I see.
Yep, skip level is just "unlock one map higher than you have already opened" and multilevel is just "choose a second map to play at the same time as you play another one". Btw, as soon as you finish one of the multilevel maps, you can't go play new one before finishing the second. Like, it is wise to go with multilevel and start two different maps with 0% progress than using multilevel, while playing 50%+ completion on the map you are playing now. People suggest to skip at first as much as you can, finish map you're playing now, then begin new map and use multilevel on another map.
Also, I've been critical of some of the updates, particularly how the artifacts have lost value/effectiveness. Don't know how happy the mods/owners are about that. I spend money here, nevertheless, so maybe still . . . throw me a bone.