The above post is all you need to know really.
Recovery missions aren't "random". If they were, it'd be like looking for a needle in a solar-system sized haystack.
It's always a case of going to a system, scanning the nav' beacon (or honking with an advanced scanner), getting a mission update telling you EXACTLY where to look, going there and loitering for around a minute, until you get a specific message saying "mission objective located" (or something similar to that).
If you see a signal source but you don't get the "mission objective located" message, it's not what you're looking for.
One thing that sometimes trips me up is that I'll take on a recovery mission, follow the instructions, mooch around in orbit of the target planet, fail to locate the mission objective and then, upon re-reading the mission summary, I'll realise that the mission objective is actually on the planet surface and I need to land and collect it with an SRV.
You can double-check whether this is the case by looking at your navigation HUD too.
If it shows a destination planet with a POI icon next to it, you'll be picking up the objective in space.
If it shows a little square box and a destination site with a POI icon next to it, you'll need to land and pick up the objective with an SRV.
None of which should ever be an issue if you don't have Horizons installed, of course.
Anyway, point being that I find it's useful to build a ship specifically for recovery missions.
I'm currently using a Viper 4 which can be nicely fitted with a #4 cargo bay and a #4 dual SRV bay.
I also have a Diamondback Explorer similarly fitted too.
They're small, fairly manoeuvrable, ships that can scoop cargo in space easily, land and deploy an SRV if they need to and they can take a bit of a beating in case you get ambushed while collecting the items and need to make a hasty exit under fire.