Hi @Anonymous, many thanks for posting this case and apologies that it has taken so long to be addressed. Yes, this has definitely been a problem since the inception of the feature tree within Fusion modelling. I guess that it's a throwback to the days when Fusion was purely direct-modelling software. It works okay for editing within a session where the loft features have been created in the model, but nothing beyond that.
This issue has now been fixed. Once this fix has made it to release, any brand new models made by a user with loft features that possess mapping data will automatically work as expected, i.e. allow immediate and correct editing of the loft mapping after re-opening the model.
Any 'older' models that possess loft features that have mapping data can simply be opened, then a 'compute all' is required to generate all the relevant caches, and then it can be saved. Re-opening this model will then allow immediate and correct editing of the loft mapping.
Again, all the best from development.

Richard Hall
Sr. Principal Engineer
Autodesk, Inc.