Corridors with Feature Lines as baselines that disappear while you use 2021 this is related to Civil 3D not actually supporting Feature Lines as baselines. This one is more of a workflow consideration for you. Your potential use of a custom Part Catalog that is not provided as part of the deliverable (or the recipient's use of same, without providing to you to do the work) Language Pack is causing fatal errors I don't understand this one, but I'm told its a known issue and something related to the fact that Civil 3D supports UK English, but AutoCAD does not.
That said, the only version incompatibility issues I know of are:
Not sure that I understand Civil 3D 2019 & 2021 (versions) both use the same 2018 DWG format.
