When creating custom blocks that use a custom geometry that contains a model larger than 16x16x16 pixels, aka one Minecraft block, the geometry causes errors and forces the block to appear as the "update" block.

Here is the error message:

[Blocks][error]-geometry.testblock contains 1 boxes outside the error bounds of (-0.01, -0.01, -0.01) to (1.01, 1.01, 1.01)

Additional info by ReaperX5

This problem did not exist in previous updates if a block was larger than 16x16x16 (unit cube) or had a bone that exceeded the 16x16x16 bounds by as little as 0.001 pixel; the geometry file would continue to load normally, but an error message would appear (which is preferred to this new way of handling larger geometry files)

This new method breaks MANY addons... it would be great if creators had the option (like in previous versions.) and weren't forced into making blocks use separate geos (if larger than 16x16x16).

It should also be noted that several vanilla blocks break the bounds, including (but not limited to) lecterns, spore blossom, walls/fences, and open shulkers boxes.

If intentional, it seems unfair that vanilla blocks are able to break these bounds while modded blocks cannot.
There was also no mention of the change in the changelog, or a reason as to why the change was made.

The current warning bounds are also incorrect (reports -0.1,-0.1,-0.1 to 1.1,1.1,1.1, when in practice this extra space is not included; actual bounds are (0,0,0) to 1.1,1.1,1.1. (1,1,1). Prior to this update, the warning was (-0.5,-0.5,-0.5) to (1.5,1.5,1.5), which makes much more sense. (Given the fact that vanilla some blocks break the 1, 1, 1 format by half a block at most)

As a final note, custom block geometries on Java Edition can be as large as 3x3x3 (blocks, not pixels). This was how bedrock was before this update...