Hey Gaetano, that looks like it might be a coordinate system issue to me. When you’re dealing with TLEs you need to be especially careful.
As a tip, you should always start by plotting your measurements against the expected measurements from “ground truth” (here, your TLEs would be OK), to make sure that you understand your data. If the obs and the TLE don’t really line up, then you have to figure out why. Once you know your data, then you can try OD.