Rule is triggered based on my last comment is this thread Binding not yet ready in startup sequence, how to detect, which is based on nyholm solution here OpenHAB3 Start Up Issues - Race Condition? How to Sequence Startup? - #13 by nyholm as it is the only solution that was working on my system.
I have read your comment (not have link now) how difficult it is to organize start as lot of things happening in the background that openhab has no control and even worse no visibility if, in what order and when they have started/finished loading.
Fully understand this is significant limitation with high impact, but at the end it renders into significant issue for the system to work properly. Also read about the runlevels, that should help, but from my point of view they are adding another layer on the same ‘confusing’? basis, which I’m (personal subjective opinion) not sure if it increases or decreases level of randomness during system start taking into account all the various errors I have seen (including java garbage over 2 monitors 
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