So, just to make things straight:
- After "Enviar conviets" sends a message to the other pool it partially passes the steering of the process (including a message) to another lane in your pool.
- Then within the responsibility of that other pool two activities are performed ("Recebar convite..." and then "Submeter proposta...")
- In parallel the original lane waits for receiving the message within activity "É informado da submissão...".
- After all 3 aforementioned activities (two from other lane and one from original lane) are completed, the steering is returned entirely to the original lane and the activity "Avalar proposta..." is performed.
If so, then you need to link directly "Enviar convites" to "É informado da submissão da proposta de tema de tese".
In general, the control within one pool can go to different lanes. It doesn't break the flow. The activities within the same lane do not have to be continuously connected as long as there is connection across all lanes within the pool. On the other hand, the connection through messages leading to other pools doesn't ensure the continuity within the pool so there has to be a link within the pool leading from sending to receiving the message. The problem is there is no link (other than the messages to the external pool) linking the activities of sending and receiving the message, so this flow is broken.
In practice, your process doesn't stop while you're waiting for the response. This is what the (currently missing) arrow represents. Think also of other options: what if the response never comes? Do you wait indefinitely or is there a "timeout" (e.g. proposal deadline)? This shows best that there is something going on in the process, even if it goes into idle state for some time. Show it with the flow arrow.