Regarding Observation 512869 …
It looks like APRS but it seems a bit too wavy regarding to the age of the TLE (21 hours).
I saw other similar observations from the ISS.
I often order my observations 48H hours before the actual moment. Could it be that, especially in the case of the ISS (big chunk, heavy drag, no TLE propagation) ?
73,
Given your station (omni antenna) and the fact that those signals are not fading away at start and end, I am ready to bet that those are local APRS transmissions trying to reach ISS. It would explain all the attributes we are seeing (doppler but not accurate, not fading, not on all observations etc)
according to ariss.net, the ISS digi hasn’t been active for 7 days. I also believe this is terrestrial (tried running it through direwolf, no decodes).