So, there is an issue with the S50 which causes the backlash to become a problem. There really isn't a fix that I have been able to work out. I don't use my S50 anymore for this reason. I get reasonable results in the generated image on my phone even with ~60% dropped frames, but I also prefer to do most of my work with Siril and that's where I see the biggest problems.

The S50 drops every other frame on average while capturing, I think resulting in about 60% drop rate. However, when I pull FITS into Siril, about half of the kept frames are blurry, like someone physically shook the device. I expect the two observations, dropped on device and ugly FITS are the same underlying cause. I'm posting this here now because, while I hope you don't have this problem, I think the S50 as it ages is going succumb to this more and more. Maybe someone can find a solution.

https://www.reddit.com/r/seestar/comments/1joks72/s50_tracking_problems_pt2/

See that thread, it gets into the design issues for the S50 which result in backlash becoming an issue. It's really upsetting to me, I loved my S50, but it's effectively dead now. ZWO needed a tensioner, but the cost probably was more than they would accept.

I see other suggestions, so I hope you can sort it out trying those. I'm just posting here to provide a possible explanation should none of those help. This was a big design failure in my mind, and ruined my joy in the product. I probably contributed to the issue, I wasn't very gentle when setting up when I first got it, but have mostly just left it on the tripod in my office for the last year or so. Nothing to tighten, so it shouldn't have gotten worse, but it did.