As mentioned this campaign has been built in DBW 1.71 and makes intensive use of CY6's C&C Mod, and not all those features are implemented in 4.12 and/or CUP. That could be the reason. But as I don't have CUP I don't really know. Sorry
Its not about features not implimented Peter. - 412 code actually BREAKS some of the C&C features. We have most of them back now and workarounds for those features, involving AI detection code, broken by TD's 412. 412 is such a step forward that we felt forced to accept some compromise but CUP does view further TD patches with great caution as a result.
Why compromise but move to 412? With Seaplanes specifically, for example, 412 allows us to place them at a predefined spawn anywhere we want to! This makes for dynamic airfields and particularly good Seaplane bases. With a few tweaks here and there your Sunderland campaign for 412 CUP will be better than ever and well worth converting.
This is a great addition to Il2. Thanks to all involved. All it needs now is a set of missions of the quality it deserves.