Ok, it has already been said but I'd like to point it out even better.
What is the UA? Look at it, remembering those concept art drawings that Han_Zen posted some posts ago.
https://forums.frontier.co.uk/showthread.php?t=162998&page=56&p=2519525&viewfull=1#post2519525
In particular the Cargo Pod Stacking thing.
For me the UA is a kind of DISPENSER of something, and it is something not good at all: those 12 pods are just waiting to be released or to release their content! And it is not a good content indeed, in my opinion.
Remember that the Human Race got rid of the Thargoids with a VIRUS. So it could be a Thargoid kind of revenge, or even better, it could be a specimen of the HUMAN VIRUS DISPENSER!
What it does? It transmit in morse code the nearest System or Station name.
Why? To ask for instructions: is it the system I have to "plague"? It is going on with its duty, waiting for instructions that will never come anymore. It is a LOST human VIRUS POD DISPENSER.
Look at those systems where a plague is spreading without any apparent reason. Perhaps something ACTIVATED one of those UA, and the VIRUS was released.
That's why we find them in a military convoy: because they are bringing it back home.
The only thing that confuses me is its strong "Alien look". That could make us think that it's simply an alien thing. So perhaps it is, or it was simply built like that to not make Thargs suspicious about it...