Trying to get a stable sync out of a Soviet built BK-0010 home computer

[blue lander]

I recently bought an Elektronica BK-0010, a Soviet-era home computer from the mid 1980's. It uses RGB plus composite sync, so I figured I could plug it directly into my NEC Multisync II with no problems. Unfortunetly, 99% of the time, the picture rolled vertically as if it couldn't find the vertical sync. It did briefly work for about 5 minutes and then went back to rolling, I have no idea why. I took a very quick look at the signal with an oscilloscope and it looked fine to me.

So I ran the signal through an LM1881 figuring it would clean the signal up. Now the picture is more stable vertically, but it still jumps around a bit. It's also now distorted horizontally. It's hard to explain, but it's like it's starting each horizontal line at a slightly different point, so all the text looks torn and distorted.

Could this be a grounding issue? Is there anything else I can do to clean the signal up?