Take an eCabS job to CN. Sort for one material only. Add a piece of off-fall material manually. Nest true shape x or y and it pops errors "unable to nest..." as if the added off-fall is the only sheet available, even though the material catalog contains viable standard materials with appropriate sizes. I can nest using rectangular optimization, and it will add the standard sized sheets as necessary from the material catalog.
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Win 10 Pro 64 bit on MSI Z390M Pro4
Intel core i7 9700KF 3.6GHz (OC 4.2Ghz)
32 gig RAM, NVIDIA GeForce GTX 1050 Ti
NVME SSM2HD 1TB NTFS
Your Default group has Only Use Added/Off-Fall Sheets When Available checked. This group is being used for the 3/4 Melamine Frosty white material in the job your export contained. When that option is checked, Control Nesting will only nest on added or off-fall sheets.
There is still an issue in consistency to Rectangular Optimization that the software engineer will need to look at so I'll get that reported. This is such a rarely used setting I'm not surprised no one has run into it for rectangular nesting.