Boolean issue, can't figure it out somehow

[Jaap (Jaap Riemens)]

I’m trying to connect the 3 recesses like in the top left corner. Strangely enough, the top left worked, but I can’t figure out how I did it. Tried just about all options. Who has the solution?

[Tod1d (Tod (with 1 'd'))]

The shapes must overlap for subtract to work. If they are perfectly aligned, it’s a crapshoot. Sometimes it works, sometimes it doesn’t. Edit the smaller shapes & make them overlap…

[Jaap (Jaap Riemens)]

Thanks Tod, that did the trick (and it could have saved me at least 2 hrs when i would have asked sooner)