Hit the enter key with my mouse hand and submitted Comment #1 early.
The GLTriangle30 sample is crashing due to a "System.InvalidOperationException: Unable to create shader" on both XA 5.1 and 4.20 - this is not a regression. This is isolated to a Samsung Galaxy III (US Carrier) API 4.3 device.
Link to stack trace:
QA will need to gather some more information for this.