Yup, no idea, sorry.
Love to know when you find out though…
I’m just setting this up with the default 3rd person char. And the only thing I can say so far, is it’s basically impossible to hit the door with the line trace, because the player’s in the way! 
Put a collision box on the door
and set it to ‘ignore only pawn’
I think the line trace begins from the follow camera and ignores the player because it never shows BP_ThirdPersonCharacter in the string you had me make earlier rather whats in front of the character.
Correct. But I couldn’t get my door to work until I put that box around it to block the trace.
Yeah the door requires collision to open. My door has a simple box collision set up and ignore only pawn is now set. (Was set to block all previously) Still get the error though.
The door frame is using use Complex as Simple collision not sure if that affects it in any way since both the frame and door are part of the same Door_BP blueprint.
Now I remember. That default door ( I had ) has no collision, duh…
You’ll need to set that back to what it was.
I’m out of ideas, sorry 
The guy who I watched the tutorial on how to do this had the same error as me at 7:35 but he uses the default door also and fixed it by simply adding a branch to the code as I already have. Learn How to Open and Close Doors in Unreal Engine 5 - YouTube
Imo:
- add a breakpoint at the cast and check the hit actors value.
- Show the trace in viewport: can you see it hitting the door?
We did all this…
You’re right! Must’ve skip that one. Nvm 
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There’s something else unseen going on…
From the Door_BP blueprint the collision is set to block all dynamic. Perhaps this is normal and shouldnt matter.
This code is absolutely fine. You have something else going on I don’t know about.
Perhaps another blueprint using T, or something like that. Where else is T used?
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Nothing else uses the T keybind.
Only other thing I can recommend is you zip up the project folder and put it on google drive, and I’ll take a look.
If it’s a big project, then it’s better to make a new one, and just migrate your level to that.