Ugh, still doesn’t help much, it’s just “some blueprint node failed to serialize because it’s referencing/connected to something that doesn’t exist”
(That’s what I would understand from the source).
Possible things to try -
a) try going through the intermediate engine versions, updating the project step-by-step
b) build the engine from source, run it in debug mode from VS and then when this happens you’ll have a full call stack which will show you which blueprint this is about (this is obviously quite a hassle, but will help you immensely with any mysterious engine crashes)
(if your project isn’t anything sensitive, pm me on the forums, I could run it on my machine and see what the debug says)