Do you use Java 8?
yes

What version of Minecraft do you use?
1.12.2

What version of MinecraftForge do you use?
[Forge Version Number]

What version of SanLib do you use?
[1.5.1]

What version of Clay Soldiers do you use?
[3.0.0-beta.2]

What is the issue / bug you have encountered? Give us a short description.
[Iron, string, cactus, nether brick and other core upgrades can all be put on one soldier at the same time]

How can it be reproduced?
[Give a soldier 2 or more core upgrades and watch in horror as it picks them all up]