VSCode not running kernel for large Jupyter notebook file (showing as html only)

I have this relatively large Jupyter notebook file that I've been working with. This morning when I opened it, VSCode only shows the html text, but not the notebook kernel with executable cells. Like this:

{
 "metadata": {
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.8.5-final"
  },

I've created other files in the same directory and VSCode correctly opens and renders them as Jupyter Notebooks, so I'm not sure what could be the problem with this one. I received some warning yesterday about the file size and today after I changed the file name it stopped working. I get not errors though, just the kernel not launching.

Any ideas of what could be the issue here?