Well ive found 1 in transit route and am running back to that every 15-20mins but my question is whats the frequency of these mysterious containers, do we uave only 3 total or roughly what direction should i be looking (have spacial scanner) ive searched the empire up to the outposts but still only. Found -1, granted i was searching up past the wardens (on phone can’t remember system atm)i seen the predator spawn in, was having a look, it spots me, F*** That S*** and ran home (full destroyer hold)
They spawn between 5-30 minutes, depending how much u stay at one sector to farm them, they are hardly near the home sectors, always far away systems. If u need any assistance, pm me. 
I shouldnt be saying this, but containers take about 3 minutes and 40 seconds to respawn. Take in mind that spatial scanner has 6km sensor range, learn to spot mysterious containers when they are barely vissible in the radar…i use 1 less than max camera zoom to notice this subtle color changes.
The mysterious containers rarely contain anything I need. Not even artifacts. Once in a while a bp. But usually just credits items.
Another thing that bugs me with OS is the drones are not always easy to spot. I feel they should re spawn instantly if used. Because sometimes there are several people waiting to send stuff back. OS sucks as it is with out having to find or wait for a stupid mailing drone. Maybe make a glow ball for them when they spawn or something.