Thank you for the explanation on the message restriction!
What I need to replicate is basically an interrupt mechanism that is triggered by an important message that requires immediate attention before returning to any other work. This interrupt can be triggered at any time, including multiple times, and must not prevent the termination of the process (i.e., by actively waiting for the message). After the interrupt has been handled, we either want to continue where we left off before the interrupt (this has been discussed before: Resume interrupted process - #10 by WilliamR.Alves and by yourself: Come back from eventSubprocess to the main process - #11 by Niall) or at a specific task (as depicted above), depending on how the interrupt is handled inside the sub-process.