That's not a behaviour I recall seeing reported before, and it shouldn't be possible to deploy the lift spoilers in flight, so it sounds like something that could be caused by a controller conflict.
The first thing I would recommend checking is if you have any "SPOILERS" control assignments being inadvertently triggered by your external hardware (TOGGLE SPOILERS, SPOILERS AXIS, EXTEND SPOILERS, etc.).
For reference, the conditions for automatic lift spoiler deployment are listed on pages 79-80 of the RJ Professional Operations Manual: https://downloads.justflight.com/products/JFF003765/RJ_Professional_MSFS_Operations_Manual_MSFS2024.pdf
Mark - Just Flight