I had this issue when I first started cooking a mod and found that the issue was caused by a few things. First of all and most important, I have noticed the dev kit is very picky about blueprint names. When renaming, try to keep the original portion of the blueprint name and add to it. For example, PrimalGameData_BP_mymod. I originally added my name customization to the beginning rather than the end and ended up with the same result you are seeing. Next, make sure you are creating a map that is linked to the PrimalGameData_BP_mymod and GameMode_mymod. Ctrl+S is your friend, use it often to ensure everything is being saved. Finally, compare your newly created assets with the original assets to ensure you have every reference needed. If something is referenced originally, don’t be afraid to copy it to the mod folder and rename it to ensure the data is accessible. Often time some references are easy to over look.