Ok I've been thinking this through and have possible explanations for the flaws in my previous post. So here we go:
A possible explanation for Unknown Artefacts, Unknown Probes and Barnacles and how they function.
Stage 1 - Star location
The probe creators are aware of one or more exceptionally rare elements in the Galaxy. They know these elements only occur on some Supernovae. Therefore the elements will only occur in Nebulae and other stellar clouds. However the only way to detect these elements is when they they get caught up in the next round of star formation. Thus the only way to find then is in at least 2nd generation stars (following the Supernova that created them). They know the there are as few as one in one Billion stars that contain the elements they seek.
In order to locate such stars they use Class 1 probes (what we call Unknown Artefacts). They distribute hundreds of these probes across a given area of nebulosity. The probes are made up of two key parts: a sensor head and a propulsion unit of 12 cells. The probes are very difficult to manufacture, requiring some rather exotic technology (which may include artificial biology). As such they have a very narrow range of tolerances. They are specifically designed to work in the vacuum of space and at low temperatures. Due to their cost all efforts are made to keep them functioning. If for any reason they find themselves outside of their operational tolerances, they are fitted with highly sophisticated self repair mechanisms which will attempt to use any surrounding matter to stabilise the probe.
Each probe has an effective sensor range of 500 or 1000 light years. Once deployed, each probe begins to meticulously scan all the stars within it's range. In our case the local probes were in this state when we first found them. They did not point anywhere as they were still scanning local space.
In the unlikely event that a probe detects a candidate star, it then uses it's drive unit to move to a pre-determined distance from that star and aligns with it. It then begins to transmit data about the star's location. Hundreds of probes are used in order to avoid possible false positives. When many probes make a detection they will start to form a sphere. It will not a be a perfect sphere as the initial distribution of probes is highly unlikely to evenly surround a candidate star but, it will still be a recognisable shell with all probes pointing at the same star.
When the probe creator then get hundreds of data signals from the same batch of probes, they know they have a confirmed positive.
Stage 2 - Planetary body location
It is not possible to locate the elements from a stellar cloud alone. Thus they need to wait till matter condenses into a star, which emits information, in order to find the elements. Of course, they cannot mine stars. However planets and other rocky bodies form from the same materials so it is possible that a solid body in the star system, if it has such bodies, might also contain the elements. In order to locate such a body a much more powerful probe is required. These Class 2 probes (what we call Unknown Probes) are therefore deployed directly into the candidate system. A long range ship (as that will likely be needed) is despatched with the probes. These probes have two sensor heads which are much more powerful. That cannot even have drive units as that would interfere with their operation. A handful are manually distributed in the target system. These then begin highly detailed scans of all solid bodies in the system. If a candidate body is located, they all point at it and begin transmitting data.
Possible stage 3 - Mining and refining
The host ship, which will still be in system then moves to the target body and begins a manual scan of the surface. If possible concentrations of the elements are detected in a given region on the upper crust a mining unit is deployed. These mining units are non-sentient, genetically engineered, semi-organic factories (what we call Barnacles). These objects partly burrow into the crust and become very secure. Their upper shell is designed to withstand high velocity impacts from meteorites. They then grow down into the crust in search of the elements. If such elements are found they grow long shoots back up to, and through the surface, around the central column. The materials are slowly refined as they are moved to the exposed tips of these shoots. They are then designed to be harvested and will regrow over a few days.
Because even at this stage, the chances of acquiring the elements are still low, if the mining unit finds anything other rare minerals and resources it will extract, refine and push these to the surface as well.
Other thoughts
It has been hinted that the UAs/UPs may not be directly related to the Barnacles. So these could be different organisations that own them, but they might be after the same thing.
This is all of course just speculation on my part to try and explain everything we have observed. Unfortunately it is not very scientific as it does not really suggest an experiment we can do to prove or disprove it.