ERROR: One or more cycles detected in flow graph.

[BastianT22]

The flow direction was upscaled from MERIT-Hydro by PyFlwDir package. But it still reported the error. How can I check the flow direction data? Thank you!

[verseve]

Does the flow direction map contains a pit (value = 5)?

If the map contains a pit, probably the easiest way is to check for cycles with pyflwdir. You can use this function (core.loop_indices) to detect cycles:
https://github.com/Deltares/pyflwdir/blob/076783cd979660a6706a1a9840873c8b8fc34f48/pyflwdir/core.py#L236

[BastianT22]

Thanks for your reply. I have checked that there are pits and no loop. The reason was finally identified that all pixels within the active pixel of the river must flow to pits (which can be not the same), but not to the boundary.