It happened again after I went back to the game, this time with stromatolites.
FYI, this is immediately to the south of player location in the save.

Some water canes block construction because they aren't marked for deconstruction during force-build.

01-26-2025, 08-34-35.png

Save with player at location attached.

Speculation: I would suspect that the water cane isn't "inside" the build area (of the roboport in this case) and thus not ...

I've found an issue similar to "looped belt too full to go at full speed" but is affecting non-full belts.
01-03-2025, 14-16-55.png
As you can see, the outside loop is fully compressed from the bottom left on round to the single lane balancer, but not along the bottom stretch.

Reproduction:
Use ...

I've been making a new rails book.
The current design has rails overlapping the edge by 1, thus is offset by 1x1.
If the BP is duplicated and "new contents" selected, it no-longer matches the original offsets.

Original:
11-16-2024, 14-16-07.png
BP string:
0eNqV1dtuhCAQANB/mWdsvKAu/krTNLgSS ...