When I zone an entire block (in this case a 17x7 block in terms of zonable grid), the mod will begin spawning growables as usual. However, if this leaves a 6x4 space available, the mod will stop working and nothing will spawn unless I cut out a 1x4 or 2x4 space in the middle. A 1u- or 2u-wide asset will then spawn in the remaining spots.

In terms of assets available, according to my style I made in the DSE, there are two 1x2s, one 1x3s, four 2x2s, one 2x3, one 3x2, and one 4x2.

This does not happen in the original Building Themes mod, but I prefer this mod otherwise.