Not had what you’re seeing but there are settings to restrict the Booster heater on DHW.
Have a look at this thread
It shows where in the MMI to look so you can see what your settings are.
When Octopus finished our installation the DHW was on very few degrees drop and then reheat and so on!
They are selling electricity for profit🙂
Really uneconomical compared to how we heated the tank, used for a day or two and then heated the tank and do on, when on gas.
Changed the settings in the MMI to do the same and put it in economy mode, and it’s really economical.
Run at 13.00 if on Cost tariff..