how to reproduce:
1 make a tank (for instance)
2 put some equipment into it's grid (batteries, shields, anything)
3 use this tank to make tank MK2 (you didn't have to put tank down to put items into it's grid, if you did, "deconstruct" it back into your inventory)
4 notice that all your equipment is gone - it's neither in your inventory, nor it is in your new tank's inventory or grid

Unfortunately this is a known issue, and the only way to fix it is to make the Tank MK2 not cost a Tank, and similar with all the other entities and armor that can have equipment installed.