Hello there @Tacsbul23!
Blender and Unreal don’t have the best relation, they tend to clash with each other in different scenarios, specially animations. If the mannequin skeletons are the same, the animations should lock as intended with AutoRig.
So, the first approach would be to reset export/import settings in both UE and Blender, in order to rule out any conflicts between either configuration. After that, test importing back the mannequin with your usual pipeline.
If the issue persists, please test the method detailed here, it has worked for me in other similar scenarios.