This sounds very much like how MSFS behaved before the last but one update, that introduced the 50% axis issue.
To the OP, do you have a controller axis bound to fuel mixture and is that controller set to full lean?
What happens when you start a flight is that the in-cockpit controls are NOT synchronised to your physical controls, so having fuel mixture set to full lean would not prevent the aircraft from starting up and flying quite happily…until you either
- touch the physical axis, even slightly, or
- Go to the escape menu and then resume the flight
either of these will synchronise the specific or all physical and virtual controls respectively.
Even though the CRJ doesn’t have a mixture control, it will still cut out if you move a mapped physical lever to fully lean.
You may want to either remove that mapping for when you are flying the CRJ or make sure that your physical mixture lever is set to full rich before starting up.