Hello and welcome to the community.
Without a relevant screenshot, I am only able to provide a limited reply. Feel free to provide images or anything that will allow us to see your level.
Previously I have spoken with another user about Anchor Fields which are very useful in stabilizing sections of your Geometry Collection.
A few other questions to keep in mind:
Is the Geometry Collection snapped to the floor?
Are there any other colliders present in the level?
I hope the post I have linked you provides assistance.