I have ignored this error in the past, but it is starting to get in the way of reading the output from the console for debugging purposes. I was doing some research last night and I found an unanswered thread that mentioned this could have something to do with pdxinfo and bundleID, but I am not familiar with how either of those things fit into the larger scope of the project (I started with a template by SquidGod).
Use the docs (Inside Playdate) and take a look at the part regarding pdxinfo, the file mentioned should be at source/pdxinfo you need to fill out all the empty fields.
Thank you for your response. After some reading, I am even more confused. From what I read, I am understanding that imagePath is for images relating to how the game displays in the menu (i.e. card.png, icon.png). In my case, the images that I am adding are for sprites and do not seem to fall under that umbrella.
I have all of my sprite images in a folder which is located at source/images/ and when I tried setting imagePath=images/, I still get the error when any image is loaded as a sprite.
Aha! I figured it out. I ended up needing a backslash at the beginning of the path. Instead of images/pixel_filled, doing /images/pixel_filled got rid of the error.
Hopefully this is helpful to someone else!