[clayne]

First the film, if your going from a 35mm negative, a 40x50cm (16x20) is considered just about the limit for a 35mm negative, and that's only with very fine grained and slow film, so a 120x180cm enlargement is well beyond what analog enlargements can expect from the film. For an enlargement that size a 10x12cm negative would be best.

Limit of enlargement is directly tied to viewing distance, not film grain. Nobody sticks their nose in a 16x20 or 20x24.

I agree with others here that this looks like something inherited during the A->D conversion (scanner).