I had this problem with morphs in the past, the only way I could fix it was by setting the grid lines at a fixed height and offset to project zero. Annoying. This might not even work for you depending on how you've set up both sections and elevations.
This seems to be a bug indeed. I have let the developers know, and we are working on it.
I have tried it with Morphs, and it appears even though parts of the Morph are out of range, they are still considered when calculating the Bounding Box for Grid Lines. I have checked it in earlier versions as well, and it seems to work faulty there as well, so this isn't a new thing in 21.
I have also tried with Meshes, but there wasn't any situation in which I could reproduce this. When selected, they won't show the parts that are out of range. There's either a setting in fuzzytnth3's project that I just can't find and causes this issue, or maybe after Migration it (or parts of it) was converted into a Morph? If you send me the file in a PM, I would be more than happy to look at it for you to see what it might be.
Anyhow, for Morphs the workaround in case of slopes (even though it won't be automatic) is to Set up a Custom distance for each Section/Elevation. You can do that if you select them in a Section/Elevation, and open their Settings. There was a bug that prevented you from using Custom Settings for a while, so you should install the Preview Update (5002) for this to work.
Daniel Alexander Kovacs
Professional Services Consultant
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