Management proposed to work with external freelancers, to "pick up speed so we can release these new designs sooner". We agreed, but of course we (the home team) can't have time to review their work because we need to develop other new features and bugfixes and such...
Weeks later, turns out that their changes are largely incompatible with the work we have been doing on the main branch. We are now rebasing/rewriting huge chunks of their work, probably taking as much time as it would have cost us to develop the design ourselves in the first place.