H-bridge driver circuit where voltage is higher than control ic
When creating the schematics I have inadvertently used the incorrect transistor type: "Q_NPN_BCE" instead of a BC817.

Note that the pin numbering is different for the correct transistor:


The base is the same, but collector and emitter were swapped.

As the base-emitter diode behaves like a Zener diode (~5V) this explains why voltages > 5V made the circuit misbehave and how the ESP8266s were damaged.

Thanks for any help.