I am assuming you went back to autosaves before the problem started?
Unfortunately, if you deleted some assets that the blueprint was referencing without somehow removing ALL references to it you may have broken the compiler or something. I did this a few days ago and it was a disaster.
First, never force delete. Track down all the references and make sure it doesn’t throw up any flags.
Second, never delete directly in the project folder because that is basically force deleting without any flags to warn you otherwise.
So anyway, what I had to do when I broke everything, was to manually copy and paste everything from my broken blueprint into a new blueprint. If you make a new blueprint it will only have the references you add, copy/pasting everything should work fine.
You might be able to migrate it using the editor migrate options, but when I did it I wanted to be **** sure I didn’t migrate any of the gremlins to the new blueprint so I did everything manually.
Your error message isn’t the same as mine as mine specifically referenced a blueprint and some asset I force deleted, but if you can at least narrow it down to an offending blueprint, then abandoning ship may get you past this.