It looks like the fix in the latest libacfutils didn't fully address the issue for everyone, in the meantime while we are working on a fix, there is a workaround to prevent this from happening:
In X-Plane 11/Aircraft/X-Aviation/TorqueSim BN-2T Turbine Islander/plugins/is_systems/settings, there is a file settings.cfg. Open that file, and set the line "disable_mtuploader" to "= 1" (it is 0 by default). Loading the aircraft after that should then be without issue.