Sims 4 corner counters bugging, will not let me put my corner Counters

I wonder if you may be trying to place the cabinet to close to the corner, like this image here.  You have to actually position it a little bit away before it "connects" like this image here.  With auto cabinets on, I have never experienced a failure in placing them, so if the positioning isn't your issue, then yes, we definitely need pictures of your specific situation.