Thanks to fembot, was missing 1 loadout tried this method and worked.
Thanks to emiloly for confirming multiple loadouts missing, tried it and worked.
There are 8 Titan loadouts, 2 you get through the story(Expedition & Legion), the other 6 you get by collecting their primary weapons on each level:
Blood & Rust: Tone
Into The Abyss - Scorch
Into The Abyss - Brute
Effect & Cause - Ion
The Beacon - Ronin
Trial By Fire - Northstar
xTGE posted a good video show all locations but if you miss any of these follow my method below confirmed by a few commentors
Just a little advice for some people:
At the end of the game I was missing Ions' loadout
I loaded up The Fold Weapon again and once
I went to my loadouts and Ion was unlocked and achievement popped.
I'm not sure if this works for just 1 loadout or numerous though. Please comment if you can clear this up.