ESP8266 "ERROR: Failed to initialize I2C Bus" - Scans fail, Component Add fails due to scan failure / no bus

[tyeth]

Random error on boot, but blocked my component testing. Was working fine ten minutes ago.
We should probably have a second attempt at initialising the i2c bus as it's crucial for most users / devices.

Version 110 + QMC5883P

 32 bytes.
13:40:18:410 -> cbDecodeSignalRequestI2C
13:40:18:410 -> I2C Device LIST Init Request Found!
13:40:18:410 -> EXEC: cbDecodeI2CDeviceInitRequestList
13:40:18:410 -> EXEC: New I2C Port 
13:40:18:410 ->         Port #: 0
13:40:18:410 ->         SDA Pin: 4
13:40:18:410 ->         SCL Pin: 5
13:40:18:410 ->         Frequency (Hz): 100000
13:40:18:551 -> ERROR: Failed to initialize I2C Bus

[tyeth]

Rebooting didn't resolve. Removing the QMC5883p fixed the bus so it scans again now. Maybe left chip in broken state or something, as it was able to be added back, and also successfully reinited at reboot.