I processed multiple S1 datasets with different chunk sizes, and the resulting GTC is very similar, but not identical.

chunks=1024
sarsen.terrain_correction(ds, dem, interp_method="linear", chunks=chunks,  output_urlpath="gtc_{}.tif".format(chunks))

chunks = 1024

chunks = 512

A-B image

The overall difference is very small(the image about about 0.03 max), however the issue is identical for all datasets I tested, that some parts of the image are not identical with different chunk sizes. The overall issue may be a very small floating rounding/shifting issue that is not an issue in practice, however I think it is best to document and potentially take a look at this.