Seems to be an issue similar to one mentioned in this post: https://forums.unrealengine.com/deve…de-c-templates
It esentially comes down to the loading phase of the plugin’s modules. However no one else has reported having this problem.
To make sure whether this is the issue or not:
-Go to the plugin’s folder (if you intalled it through the launcher it’ll be under “…\UE_4.21\Engine\Plugins\Marketplace”)
-Open the MirrorAnimationSystem.uplugin file using Visual Studio
-Change all lines with:
"LoadingPhase": "Default",
to
"LoadingPhase": "PreDefault",
-Save and try to reproduce the issue you were having, if it continues try changing that line again for:
"LoadingPhase": "PostConfigInit",
-If it persists change the line back to default and I’ll look into what could be happenning.
Cheers.