Had a look at mine and I think they probably could do with raising slightly. I didn't feel like tackling it as I only wanted to hem a camisole.
After a few issues, I don't think it liked the overlock silver grey thread I was using, a problem that I've encountered in the past, I think I will have a go tomorrow in decent daylight.
One thing I think is a reason (it shouldn't be but.....) for getting skipped stitches is if you stop stitching in the middle of a line and then start again. I did this and know where it was (not over a seam). When I came to check the stitches there was a part where the looper thread had snapped, it was exactly where I had stopped. I've thought for a while this could be a reason so I try if possible to keep sewing even if very slowly. Just a thought.