Plug In Dimmer on Circuit with Two Wall Dimmers Malfunctions
Firstoff, do not put dimmers on receptacles except for testing.  That is illegal and dangerous, unless you use a special magic receptacle that's keyed to reject all loads except certain lamps which you put the companion plug on.

If that setup needs GFCI protection, then you would be better off learning all about GFCI's ability to protect downline loads using the &quot;Load&quot; terminals (which you should never use for any other purpose)... and wire it so the dimmer is downline of the GFCI protection.  You can't dim GFCIs either.

However, your root problem is miswiring.  Somehow the  patio lights are in series with the other lights.
The next step here is for you to post pictures of the interior of all boxes.  Do not disconnect any devices, but do try to pull things out so we can see how the wires connect to each other and which wires are grouped into which cables.