Well, I remember when i first moved to timeline engine and my phone got rebooted I've received a bunch of empty messages with [Action] action - which at that moment I thought was bound to certain mistype in platform integration.
Since then I never got it again (neither normally nor on reboot) and i didn't manage to understand where they came from so my conclusion was similar that they were certain transient messages which slipped through watchfish monitor.
That time i didn't have pin persistance yet so there was no way i could catch them. Hoped they would be stored now but no luck again

So if anyone else is getting these empty messages with [Action] action - try not to restart daemon but instead capture logs using devel-su / journalctl or pebble SDK / Dev Connection.

BTW these normally looking json notifications - were they normally shown as notifications or you just see them stored but they weren't popping up on pebble (hence could potentially be empty malformed pins)?