@Dave I believe they are related to an SOS crash of my application.
See my post here: TCPClient unstable in 0.4.6
The code can be found here: https://github.com/mhaack/Particle-Photon-Apps/tree/master/plant-monitor
If I comment out line 122 in plant-monitor.ino the application does not crash any more the the mysterious events are gone as well.
Markus