This is an issue with how werl updated the mod name.
I fixed it by editing one line in a file inside the mod zip file. In "construction-train_0.3.0/prototypes/construction_wagon.lua", line 61, change
icon = "__construction-train__/graphics/technology/ct-construction-train.png",
to
icon = "__construction-train-werl__/graphics/technology/ct-construction-train.png",