RRA trigger,
The disconnector is binding up in the trigger, and the light primer strikes are actually the hammer following the carrier back down closed. The same causes the bursts, but the disco is holding the hammer until the bolt slams closed then the hammer is freed.
Pull the trigger and make sure that the disco is moving freely in the trigger, and not binding on the pin. This binding is both the no second stage problem, and the doubling/fail to fire problem.
Dropped case,
The can is causing the rifle to over cycle (read gas port too large with can, and the bolt is opening too fast with the spent case still highly pressure bound to the chamber wall). Options are either drop in a #60 O ring around the extractor spring to add tension to the extractor to assist it in dealing with the greater surface tension of pulling the more pressure bound case, or install an adjustable gas tube to allow a smaller port setting for when the can is used (read get the action back in tune with the added back pressure when the can is used).
Adjustable gas tubes go for around $60, O-ring goes for a dime.