Your armour may be damaged. In vanilla you can only wear it for so many days until you have to replace it. You are supposed to take it off every time you arent using it. If you dont want to spend time putting on armour and taking it off every time you get a raid, you need the mod "Durable Clothes".. Its up to you but personally I find it too much of a hassle getting 10 colonists put on their marine armour for when a raid happens and just have them wear the marine/cataphract armour all the time rather than change back into their parka/duster when the battle is over