Just following up on this - I tried changing the livery / variant on subsequent flight instantiations, but still ran into the engine start issue consistently. The behavior seems dependent on selecting a variant I have not invoked previously (since reinstallation of the aircraft in MSFS 2024) - if I select a variant for the first time, I can start the engines with no issues. Any subsequent instantiation of that variant will not allow an engine start.
I also tried clearing the WASM folder contents in the appdata for MSFS 2024, with the exception of the work folder, which I believe contains the license data for the RJ. This did not seem to resolve the engine start issue.
This definitely seems like a MSFS 2024 issue, as there is other odd behavior that seems dependent on whether or not an aircraft variant has been loaded for the first time (ex - avatar not being correctly spawned outside the aircraft when a flight is started on subsequent aircraft instantiations). I am currently using the SU1 beta that is currently available, but unfortunately still seeing the engine start issue. I will wait for SU2 to test again to see if the issue gets resolved. This is unfortunate, as the RJ is a brilliant plane to fly when I can start the engines :(
Out of curiosity, is there any plan to rework the RJ aircraft for MSFS 2024 to use B events as opposed to LVARs as used currently in the 2020 version? I have been flying the Inibuilds A300 specifically coded for MSFS 2024 (with full B event implementation) and have had virtually no issues with that. From the standpoint of someone configuring aircraft control mappings via tools like Spad.Next, B events are so much easier to work with.