Neff built in Oven/microwave wave guide kit

Compact built in oven with integrated microwave.
Mod Enr C67P0N3/01
Customer had just moved back into their house after renting it out for a while and microwave part of oven not working. Starts for 10 seconds then stops. Up inside the roof of oven I could see the rotating wave guide was broken. Blade missing and ceramic all broken. So looked up parts and ordered a “repair set”. I did do a check on the magnetron etc as much as I could.
When the repair set arrived along with all the bits that rotate in the top it also came with a big wave guide plate with fixing brackets that to fit to the roof in between the top element. Almost covers the whole roof part. Now I just assumed this part had been broken and removed line the other piece by the tenant. I was not familiar with what’s supposed to be there but this wave guide board wasn’t on the exploded diagram that I could see. Anyway I fitted all the new parts including the wave board but the microwave is doing the same. In fact it starts for only about 3-4 seconds and just stops and the display just goes back to before anything was selected.
Bit confused.
Any ideas please?

Thanks

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