Have you waited for the colour coding to settle? When you place a new piece they all turn green and slowly turn yellow/orange/red, if that's not the case all i can think of is that your floor may be floating and needs support to support the beams and roof, also which type of wood do you use?, core wood is stronger than basic wood and offers more support so you won't need to fill your house with beams, also from personally experience i try to build a chimney in the centre of my house to offer support, if it's a bug i can't offer any advice sorry i hope this comment helps

P.s about the floor you'll want it to be blue, if it's green it's floating