SOLVED: Construct support fixed my project. It was one layer that I had previously named "?" in C2, where this project started before opening it in C3 to continue work there. C2 seems to have allowed "?" as a layer name, whereas C3 will give an "Invalid name" popup if attempting to name a layer that. Thank you!
I read previous posts about the "invalid names" causing this, but don't see how this console log tells me what those are. I sent my project to supportrsm@construct.net to be fixed, but if someone can tell me how to fix it myself, and I fix it, I can let them know I no longer need help with it. Thank you
Note: This project doesn't even open in previous versions (I tried r388.2, 388, 387, 386, 385, 384, 383, 382, 381, and 380) so I wouldn't be able to change any names of anything inside the project, but I do have it saved as a folder project, so I can edit anything if needed that way.