Ah well that correlates well I guess.
I have noticed similar behaviour (at least from the sensors), but I still used backup heater during that time and it was unclear if the ESBE valve was actually opened as the flow temp dropped so much:
I changed the logic for mine, as I was incorrectly tagging the DHW ON for defrosts to:
espaltherma_dhw_on:
friendly_name: "Altherma DHW On"
value_template: "{{ (states('sensor.espaltherma_iuoperation') == 'DHW') or ( (states('sensor.espaltherma_iuoperation') == 'Heating + DHW') and (states('sensor.espaltherma_esbe_valve') == 'ON') ) }}"
Previous was
# value_template: "{{ states('sensor.espaltherma_esbe_valve') == 'ON' and states('sensor.espaltherma_defrost_operation') != 'ON' }}"
I have a hydrosplit unit so behaviour likely to different with backup heaters etc.