Bug: Topics that span multiple slots can hide existing topics

[LXBdev]

1. Create a room
2. Create two slots
3. Create a first topic that requires one slot and put that into the second slot
4. Create a second topic that requires two slots and put that into the first slot
5. the first topic is no longer visible and cannot be interacted with

Solution ideas:

• Show it as a conflict in the UI, allow interaction with the hidden topic
• Show a warning to the user that they are about to cause a conflict