I have also seen other issues where the empty HTML causes crashes. If I create a custom summary element that only allow paragraphs with bold and italic text using addChildCheck and addAttributeCheck I also get into the situation where I have an empty HTML element without attributes that then crashes.

Does the case you mention also relate to the Remove format?

No that is just addChildCheck and addAttributeCheck that ends up removing all attributes from the empty HTML elements when I paste in content to the constrained element, the model can't handle empty elements without any attributes it seems, so it crashes.

I made a branch showing how a constrained element can cause a crash.

Originally posted by @sunesimonsen in #18089