I am also getting that same error. But I don’t think it is related to entering PlayMode(I might be wrong). I get it whenever I reload the domain(when the Reloading Script Assemblies window appears). I use Enter Play Mode Options and have domain reloading turned off and it doesn’t appear when entering Play Mode, only when reloading the domain. Could you try it and see if it’s the same for you?
Here are my repro steps:
1. Make a new FSM.
2. Create a custom ActionTask.
3. Assign that action to a node in that FSM.
4. Override the info property inside that ActionTask.
5. Write code that encounters a null reference exception(any kind of exception will probably work) before the return statement inside the getter of the info property.
6. Recompile. A bunch of errors will appear(as they should). The Node with that action assigned will look all weird.
7. Fix the code so that it always returns something.
8. Recompile. The errors in the screenshot will appear, even though your code is fixed. The errors will appear whenever you recompile(reload the domain) for the rest of that Unity session(if the Canvas window is visible).