Loading Entity Scene failed because the entity header file couldn't be resolved

I recently switched to using ECS to manage bullets in a bullet hell game and the performance gain is well worth it. I have a single subscene in my game scene that holds references to prefabs used to create bullets or items later using a MonoBehavior.

The problem is occasionally when loading into that scene in the editor’s play mode it gives me the error “Loading Entity Scene failed because the entity header file couldn’t be resolved. This might be caused by a failed import of a subscene. Please try to reimport the subscene SubScene from its inspector, look at any errors/exceptions in the console”. I don’t know why or what’s causing it to complain like that and the error only goes away after I restart Unity about 75% of the times.

I have been using the Entities 1.3.2 package up until today when I updated it to 1.3.5 but it still happens. I have also tried looking at previous discussions about this matter to no avail. Does anyone know why this is?