Not a stable object – how you can repair for subtraction – SketchUp

I believed I had made this stable however apparently I’ve not. This was all executed with extrusions. May somebody assist present me what I missed?
Wheel Lock.skp (172.3 KB)

I’m unsure however I feel you want to delete the faces half approach down the holes. If that’s incorrect I’m sure you’ll get an accurate response.

spot on @Guido

I grouped it, ran stable inspector, and lo and behold, there was a face inside.

now it’s gone, it’s stable.

Wheel Lock 2020.skp (185,0 Ko)