Hi. I'm reaching out to see what brakes you've installed on your FM138. I've been discussing this with Malissa from HongFu and there seems to be an ongoing issue with Shimano brake compatibility. Specifically, the M6120, M7120, and M8120 series are not recommended. Additionally, a customer reported difficulties installing a rear XT M8100 brake. Malissa suggested exploring SRAM brakes as an alternative. While this seems unusual, I won't be able to verify the compatibility issues with Shimano brakes until I receive the frame.