We were both diving rEvo micro's. We discovered the problem during the bubble check, but we had delayed the bubble check by 5 min because the lake bed was at 2-3 m, and visibility was ordinary. So we did the S drill in 10m, I went first no probs, when it was my buddy's turn there was a the torrent of bubbles coming from under the lid of his revo, I signalled to go the the surface.
My buddy was moving a bit slow in ascent (more like 1 m per minute), bubbles were still coming out from under the lid, and I was worried about his unit flooding / caustic / weighing him down, so I signalled him a second time to switch/bail-out and ascend.
I was told that the unit held a neg in the build, but that it was a weak neg. Back on the land, there was no water in the unit, but the unit wouldn't hold a neg. So maybe my recommendation to bail-out was a bit conservative, but after only a 120 CCR dives, I have never seen more bubbles coming out of a re-breather, there was an obvious problem.
I was told with some removed, cleaned and lubed o-rings at home and the neg was restored. Maybe one of the large o-rings around the revo lung well had rolled when the lid was put on. In hindsight it was a pretty easy fix, that could have been done it in the back of the SUV on the shoreline.
We also had a bit of a re-awakening about lubing o-rings. The manual says at a "minimum the interval between checking and greasing should nevertheless never be longer then one month." I think this is now being interpreted by us as "remove o-rings, clean and re-grease at least once a month."