Colliders suddenly refuses to work

Hello,

I'm following a 3D youtube tutorial and have completed it. I've added walls so my cube doesn't go off the road but my walls don't seem to work. I've done the following:
1 - recreated my object to make sure it's not an unexpected bug. In the past, recreating an object solved the problem.
2 - Checked youtube and other projects i created and followed whatever components were required. Unity's roll a ball tutorial was used as part of the example. My colliders still won't work.
3 - Checked the Unity LTS 20203.14 and 3.17 manual and box colliders are what they should be. I've played by inserting / removing rigidbody but it doesn't help.
4 - Since this is a very basic item and worked in previous Unity LTS and non-LTS, I'm unsure why it suddenly just won't work.

I'm not sure what else I should do.

 

The issue is solved. It appears that there is some strange inconsistency in the is trigger checkbox. Sometimes for no reason, it just doesn't work. Information has been provided to the unity QA team so this case can be ignored - unless anyone has useful things to add.