Unity's layer-based collision can exclude colliders and triggers from interacting with each other at all.
Check that the toggles matching the colliders layers are enabled in the project settings.
See , and the Layer Collision Matrix at the bottom.

See Layer-based collision detection for more information.
Individual rigidbody components have layer overrides that are merged with the global settings.
By default, include layers and exclude layers should both be set to nothing.
If you are using these settings, be aware of their impact.