As above your diagram would appear to work. If I was there it would be straightforward to test, but for now there are some quick checks that can be made.
Turn the electricity off.
First, check that the screw terminals are gripping the copper, not the insulation in all terminals, give each wire a gentle pull to make sure it is gripped.
If that is all good, at the dimmer switch, the side that is not working, mark the yellow wire from terminal L1 with some tape or similar so you don't forget it. Disconnect this marked yellow wire and connect it in with the 2 wires in L2, tighten terminals L1 and L2. Switch the electricity back on, the lights that didn't work before should now be on permanently. If they are on, then either the dimmer is faulty or the switch at the other end.
Switch off the electricity and return the yellow wire back to L1 where it came from. Replace the defective dimmer/switch.
If the lights don't come on, the fault could be elsewhere. If you mixed up the 3 cables the lights would not behave as they are so I don't think it's that.