At least for me, this is due to 2 things:
Thing 1: For the first 20-or-so uses, the Plug-It cord and it's receptacle is a little sticky. This will improve over time.
Thing 2: The Plug-It cord connection on the TS-55 is in an awkward position and/or orientation for all but small hands. I've skinned my knuckles a few times on the top of the baseplate trying to twist on a power cord. This is a simple matter of ergonomics and should have been caught in the design phase of the product. It can be fixed by angling the Plug-It receptacle as little as 15 degrees in the "up" direction. Hopefully we'll see this on the next saw...I swap tools, not cords, so it's continually an issue for me, though maybe my hands are towards the large size so I feel it more.
For the first few "plug-ins", I had to use the fingertips of both hands to get it to lock. Now it's much easier, as long as I'm careful.