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Please see the official X‑Plane Support page for help.
I can add a second monitor and not see a crash. Make sure you remove all plugins then if you can still create this, send a screenshot of your graphics settings, the log.txt and the exact steps you take to see the crash (including everything you click on, numbers entered, etc) to the bug reporter.
The rather chilly response from X-Plane regarding multiple gpus....
"Jennifer Roberts <firstname.lastname@example.org>
Mon 11/13/2017, 4:35 PM
X-Plane does not and has no plans to support multiple graphics cards. If this worked previously, it was chance and we do not provide support for this configuration.
email@example.com"So basically plug all monitors into one card, if you have more for scenery, X-Plane has no intention of acknowledging you. Win some loose some I suppose.
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