QGIS Geometry Generator expression to approximate rock outcroppings

gistfile1.txt

with_variable(
	'segment_len',
	11, -- the length of each segment
	collect_geometries(
		array_foreach(
			generate_series(
				0, length(boundary($geometry)) - @segment_len, @segment_len
			),
			with_variable('offset_inner',
				offset_curve(
					make_line(
						line_interpolate_point(boundary($geometry), @element),
						line_interpolate_point(boundary($geometry), @element + @segment_len)
					),
					rand(1,11), -- range offset of the inner boundaries
					1
				),
				with_variable('offset_outer',
					offset_curve(
						make_line(
							line_interpolate_point(boundary($geometry), @element),
							line_interpolate_point(boundary($geometry), @element + @segment_len)
						),
						rand(12,30), -- range offset of the outer boundaries
						1
					),
					collect_geometries(
						@offset_outer,
						make_line(
							start_point(@offset_inner),
							start_point(@offset_outer)
						),
						make_line(
							end_point(@offset_inner),
							end_point(@offset_outer)
						)
					)
				)
			)
		)
	)
)

Update: It was my version of QGIS in the end. Upgraded to 3.14 (I wish they'd use leading zeros) and it worked without issue. Thanks!