Logarithms pose uniquely thorny issues when using difference-in-differences. When the baseline difference between your control group and experiment group is large enough, using a logged dependent variable can actually change the *sign* of the estimated effect!
Logarithms are ubiquitous in economics. They allow you to conveniently express percentage changes. However, your data includes a zero, the log representation breaks. It turns out that there is no solution fully robust to the choice of units used! 1/