It took me ten years of playing Sins1 to get the "Get all the artifacts in the game in one match" achievement because it required luck and a huge map, and my computer wasnt nice enough to run huge maps until recently.   That particular achievement in the vanilla Sins2 probably requires several matches on huge maps, just like my experience with the old Sins did, AND you should play the biggest maps you can run without winning the match before researching all 200 planets.  

I think the Raider achievement is broken. The game shows the resources gathered while the raiders are attacking, and I recorded at least 30,000 before before I killed the last AI in a game. I created a fleet of them just to do that at the end. No achievement popped up while I was playing or after the game ended.

Regarding the 4 artifact achievements - the best way I found to do it is on an 8 player map with only 1 easy AI. You quickly kill the AI, then capture all the planets and explore them until you have all the artifacts, then put them on one ship/planet. When I did this, the AI had actually gotten the data archive before I killed them, but they put it on their home planet. So I captured their home planet, then found the other 3 and placed them there as well to get the achievement.

Currently I cannot speak to if an achievement is impossible, as I do not know. However the team is aware that some achievements are showing issues and need to be addressed, this is unlikely to be looked at in detail until the team is back from holiday in January though for clarity. I am collecting a list of achievements people believe have issues, if you have others youd like noted

As an update on this - I was able to make it work by doing it in a new game. Makes me think it is something about saving the game that messes it up. I noted that on the discord achievement bug thread.

Regarding Military Intellegence - you are allowed to research the civilian ones that are needed. I researched all military topics, then researched "Evangelism Node" to unlock the last military researches. Then I did no further research and won the game - the achievement popped with the win screen.

Space Ponies is just a random planet bonus - max surveying on all planets over the course of your games and you'll randomly get it eventually.

As it is, I have all achievements, so they are all possible - but I did run into bugs as noted above. Things like Military Intelligence definitely suffer from not being well explained.

Thank you guys for the updates, ive seen similar reports from others that im sharing with the team

Thanks Vecctor, was able to achieve it following your advice.

Update to the above post - I did try editing but it didn't seem to take.

I played Lithor Cluster (1v1) as TEC Primacy to test Privateer again and Military Intelligence. Neither worked. No saving or reloading in case this messed with things, though I did alt-tab again for something or other. 

I recruited exactly 500 supply in Pirate ships - in the off chance a perfect match rather than over 500 is required, but the achievement failed to unlock.

Likewise for Military Intelligence I researched all tech I could but had to research Quarnium Forging (Civilian III), its requirement of Exotic Refinery (Civilian II), and Huge Cargo Hull tech for Deep Space Trade (Tier 4 Starbase tech). I'm not sure if it's any civilian tech, or the Quarnium Forging\Exotic Refinery that glitched it but barring Titan farming, or a huge map that gives Quarnium for Surveying, this seems another impossibility. According to https://strategywiki.org/wiki/Sins_of_a_Solar_Empire_II/Resources Quarnium may be found via surveying gas giants - which require civilian tech to colonise, and desert planets - which require civilian tech to colonise if not Advent.

Obviously some people are managing to unlock these achievements - 0.4% of Global have Privateer, 0.1% have Military Intelligence - for comparison purposes only 13.3% have Ensign (play 10 hours), but given my own experiences I'm not sure how they manage. 

Thanks for the advice Vecctor. I trialled another match - Easy AI defensive ally v 2 Easy AI defensive enemies on Shuriken (4p). It was quite painful and slow waiting for my ally to acquire exotics, indeed I thought the game would end before I managed to get the last few, but it did work out. I never officially did any Empire research, I just built 4 Empire Labs then queued the Serevun Overseer military techs that required Empire I or whatever it was.

I'll probably suggest to friends that if they want the achievement that 1 goes for the achievement while everyone else funnels them the necessary materials - IRL allies will be far more responsive!!!