If items to be compiled are explicitly de-selected in the database compiler (e.g. because another colleague is using it as well), the "WaitForCompiler" is removed from the DBQueue at the end of the compile, but DialogScriptAssemblies with IsValid=0 remain.
This leads to no more schedules being executed. The main flaw is that the user does not notice this.
This is a product defect (31832).
This will be fixed in a future release of the product. If you require this immediately corrected, please contact Support for a hotfix referencing the defect ID 31832.