It looks as if (on WIndows), OpenLP starts Powerpoint when it is first needed, then leaves it running until OpenLP closes, keeping a connection to be re-used for subsequent presentations. This is clearly a sensible thing under normal circumstances, but if OpenLP crashes, for example due to the 3.1.7 crash on shrinking OpenLP windows, then Powerpoint is left running.
If OpenLp is then restarted it is unable to connect to the old PowerPoint and also unable to start a new one. It might be good to have an option to close Powerpoint when OpenLP no longer needs it to give a lower performance option but which would give an alternative to rebooting the AV PC during a service for less experienced AV operators. I can kill Powerpoint via Task Manager, but we are trying hard to recruit more AV people who have less computer knowledge.