I found out that the cause is the dynamic=true parameter of the ultralytics export function, but without it I get this error during compilation:
ERROR   : Traceback (most recent call last):
ERROR   :   File "<frozen compiler.top_level>", line 494, in quantize
ERROR   :   File "<frozen onnx_graph_cleaner.onnx_graph_cleaner>", line 864, in clean
ERROR   :   File "<frozen onnx_graph_cleaner.onnx_graph_cleaner>", line 49, in closure
ERROR   :   File "<frozen onnx_graph_cleaner.onnx_graph_cleaner>", line 80, in closure
ERROR   :   File "<frozen onnx_graph_cleaner.onnx_graph_cleaner>", line 796, in _split_pre_post_processing
ERROR   :   File "<frozen onnx_graph_cleaner.onnx_extractor>", line 212, in extract
ERROR   :   File "/home/aetina/.cache/axelera/venvs/ac95b872/lib/python3.10/site-packages/onnx/checker.py", line 179, in check_model
ERROR   :     C.check_model(
ERROR   : onnx.onnx_cpp2py_export.checker.ValidationError: Field 'shape' of 'type' is required but missing.
ERROR   : 
ERROR   : The above exception was the direct cause of the following exception:
ERROR   : 
ERROR   : Traceback (most recent call last):
ERROR   :   File "voyager-sdk/axelera/app/compile.py", line 456, in compile
ERROR   :     the_manifest = top_level.compile(model, compilation_cfg, output_path)
ERROR   :   File "<frozen compiler.utils.error_report>", line 65, in wrapper
ERROR   :   File "<frozen compiler.top_level>", line 831, in compile
ERROR   :   File "<frozen compiler.utils.error_report>", line 65, in wrapper
ERROR   :   File "<frozen compiler.top_level>", line 496, in quantize
ERROR   : axelera.compiler.exceptions.ONNXGraphCleanerError: Cleaning graph with ONNXGraphCleaner failed:
ERROR   : Field 'shape' of 'type' is required but missing.
ERROR   : Cleaning graph with ONNXGraphCleaner failed:
ERROR   : Field 'shape' of 'type' is required but missing