Zynthian hangs on PianoTeq chain startup when no USB midi attached

[Octet-nl]

Describe the issue

When I power off the Zynthian with a USB MIDI keyboard attached, and I start it somewhere else with only a DIN MIDI keyboard attached it hangs on adding the Pianoteq chain.

To Reproduce

Steps to reproduce the behavior:

1. Attach USB midi device
2. Add a Pianoteq chain
3. poweroff
4. Start Zynthian without USB midi device but with DIN midi device

Expected behaviour

Zynthian starts with DIN midi device and initializes Pianoteq chain

Actual behaviour

Zynthian hangs on adding PT chain. No button response, no SSH connection.

Screenshots

Additional context

This only happens for a Pianoteq chain.
When Zynthian hangs, I can only power down, start with USB MIDI and remove the PT chain.
Then I can start with DIN midi and I can add PT chain.

Configuration

Hardware

Raspberry Pi 5 Model B Rev 1.1
Audio: V5 ADAC
Display: MIPI DSI 800x480 (inverted)
Wiring: V5
I2C: MCP23017@0x20, MCP23017@0x21
Profile: V5_Hans

System

Debian GNU/Linux 12 (bookworm)
Build Date: 2025-05-30
Memory: 13% (1087M/8063M)
Internal Storage: 26% (15G/59G)
Temperature: 30.7ºC
Overclock: Maximum
USB/ZYNTHIAN: 16% (9.0G/59G)

MIDI & UI

Tuning: 440 Hz
Master Channel: Off
Preload Presets: On
ZS3 (SubSnapShots): Off
Power Save: 10 minutes
Audio Levels on Snapshots: On

Software

zyncoder: oram-2506.1 (e903d39) 
zynthian-ui: oram-2506.1 (a61ed16)
zynthian-sys: oram-2506.1 (9c365eb)
zynthian-data: oram-2506.1 (4a5b9ff)
zynthian-webconf: oram-2506.1 (024ff8d)