If you remove and re-add the same uniform/vest/backpack in the same frame (non-scheduled SQF execution) the gear system corrupts and doesn't register the container with clients or the server, and any subsequent calls to addItemToUniform/Vest/Backpack are corrupted and do not register on anyone but the local machine in which it was called.
Introducing a delay fixes the issue, but this is a hacky workaround.