leosutherland wroteI have the following scenario (using v5.5.2):

It's a 4 bar loop of a chord. In this case, using an instance of Memorymode (the instrument is irrelevant since this happens with every plugin I've tried). There is a volume automation that starts with some volume value, then cuts to to zero where you would expect. In the channel, the automation is set to Read.

............. for every loop thereafter. Moving nodes around in the automation lane makes absolutely no difference to the volume (and yes, automation is still Read).

........Until I hit the space bar two times (or the Play/Pause button on my FP2, or the onscreen Stop and play buttons) - at which point the automation kicks back in and I get the sound-silence cycle as before - until I select another preset.

Possible cause worth investigating.

The channel automation you say is set to read. Channel automation will only follow the channel volume (or channel pan, or channel related) so perhaps you just stated that to show the channel volume is reading as it should and is out of the picture of what is going on with your event automation (shown). Event information can be quirky in such start-stop-return by stopping twice, etc. Even from instrument to instrument. I'll combat those kind of event automation anomalies by always returning the automation to its default position. Then pick it up from the next event the same way.

So let's say a parameter defaults at some central position, and its default automation is shown at center (horizontal line at center). Then no matter how you draw the automation, have it return to center rather than trailing off at some other position at the begining and end of an event. This also helps because if the event shows up later in the song, it can pick off the same position or from its default position. You can also view the parameter of the control you're attempting to automate. There's an outside chance that the automation is conflicting with instruction elsewhere. Where? Possibly right at the end if the event, so make sure it's not interfering by opening your event a little more and checking there.

Again, event automation does perform a little quirky at times, so where possible, try to "steer" it back by drawing it in whenever possible. Yes they'll even be times that redrawing automation won't affect the change. This may be a case if different plugins/instruments have different parameter instruction, or conflicting MIDI CC, etc.
Hope that helps.

Lastly Leo, your attachment shows the "Outputs Master" tab. It may be conflicting with another output. Check the neighboring tab (Master Volume) and that it isn't also using volume automation. I'd really avoid using a plugin parameter for main or master output level of its own level for both the quirky event automation noted. Besides, that's best served with track automation. Just sayin'. Such event automation (particularly having several volumes selected in a event) may invite problems. Mmv.