USB-C bus-powered hub causes external MIDI keyboard key repeats and dropouts on MacBook

Environment

MacBook Pro 2019 running macOS 12.5, bus-powered USB-C 4-port hub (no independent power), connected to a USB MIDI keyboard (class-compliant), DAW (Ableton Live) running low-latency audio buffer of 64 samples. Direct connection to MacBook USB-C adapter works fine.

Symptoms

When the keyboard is connected via the bus-powered hub, some played notes repeat rapidly (stuck note) or are dropped during fast passages. MIDI input in the DAW shows bursts of duplicate messages and occasional large gaps. When the keyboard is directly connected (bypassing the hub) the problem disappears. Other low-bandwidth USB devices (mouse, thumb drive) appear to work normally through the hub.

Observations

Console logs show recurring AppleUSBHostPort warnings and occasional 'device not responding' entries correlated to the repeats/drops. When the MacBook is on battery, the problem frequency increases. Switching hub ports or using different USB-C cables changes the behavior but does not eliminate it. The hub is bus-powered and also connected to other devices (external SSD, webcam) at the same time.

Already attempted

Tried different USB-C cables and ports, removed other devices from hub leaving only the keyboard (improved but didn't fully resolve), SMC reset and NVRAM reset performed, macOS updated to latest patch, tested keyboard on a Windows laptop via the same hub (behaved poorly on Windows too). Updated keyboard firmware where available. No changes to kernel or driver settings were made.

Question

How can I stop MIDI key repeats and dropouts when using the hub without replacing the hub, and how to identify if the root cause is power delivery, hub bandwidth, or USB host power management?

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AI DIAGNOSTICS

Incident analysis

Updated 1w ago• Trouble ID

Most likely causes

Hub does not provide stable +5V power for sustained USB device operation (bus power limits), causing device resets or retries. 85%

Hub internal controller firmware bug or poor USB transaction scheduling causing dropped IN endpoints. 65%

Host USB controller enters a low-power state (USB selective suspend) and the hub/keyboard do not handle wake reliably. 40%

Summary

Bus-powered hubs may not supply stable power under bursts or may have hub internal hubs/controllers that increase latency or drop USB transactions under load. MIDI devices are sensitive to latency and packet loss; duplicated messages and 'device not responding' logs point to the hub intermittently failing to service the device. The issue worsening on battery suggests host-side power management also participates. Because the hub also showed poor behavior on another host, the hub hardware or firmware is the most likely root cause.

Suggested Fixes

Diagnostic step 1

Use a powered USB hub that has its own external power supply and test keyboard behavior. This is the simplest reversible test to confirm power as root cause.

Diagnostic step 2

Remove other devices from the hub and leave only the keyboard; test with MacBook connected to mains power (disable MacBook battery-savings mode) to see whether symptom persists. If stable on mains with single device, power budget on bus-powered hub is implicated.

Diagnostic step 3

Check System Information → USB when keyboard is connected through the hub and compare the reported speed and current draw vs direct connection. If the hub reports the keyboard as 'Low Speed' or shows power warnings, that's indicative.