_.padleft
So in less than a year "padleft" came and went away because all strings don't start on the left and someone decided that "left" means "start" except that the reason that it doesn't is the reason that it was changed. Even worse, the 4.0 documentation does not document that _.padstart renamed _.padleft. It's hard to grok what cannot be grepped.
Why blame someone for depending on padleft in a world where libraries swap out abstractions in less than a year? Breaking changes are bad for other people. Semantic versioning doesn't change that.
Dropping the this param with no period of deprecation? Pretty breaking change to make with no warning. Renaming first/rest to head/tail? Was it really worth it? Particularly when they go the opposite direction of replacing traditional functional names with more explanatory names by removing the foldr alias for reduceRight.
All this in a language that doesn't make it easy to do automated refactoring means that you basically break everything upgrading to Lodash 4.0 so you can't refactor parts to the newer style piece by piece.