This is when first lockdown strikes. It inevitably halts things to a pause. The client is asking to take a break, it isn't clear how things are going to turn out. And there is one other thing.
Once the estimate is signed, the prices get fixed. However, during lockdown any delays from the suppliers or other limitations may lead to price rises for materials for instance.
Luckily for us, when the first shock was withstood and we realized that lockdown was not an excuse to give up on a dream, and thus, we continued with works. A setback of a couple of weeks had little to no effect on deadlines.