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Great news that it worked for you.

I hope it stays working. I wonder if you always need to use the standard resolution on an iMac and/or MacBook or it was just a coincidence that triggered something. I fear a little to change it again and leave it for the moment at that resolution.
 
I did just a bit of testing. I can't get it to malfunction by changing the resolution of either computer. It would be great to figure this out. I am not confident it will keep working, even for me.

When I was having trouble, I did find posts discussing Universal Connect only working intermittently.
 
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