Morphy Richards 48268 Breadmaker - bread size sudden decrease?

Bought this Breadmaker 1 year ago. Have done probably ~70 breads on it. 95% of the breads had same recipe.
Use 3 different flours: Allison strong bread, Hovis strong bread and Lidl bread flour.
The bread has been always growing above the pan size (~20cm) and gone back to the pan size as a minimum.
Suddenly in June the bread started to grow only to the top of the pan and as final size being ~16-17cm....
What could have gone worng ?
I did not change the recipe or ingredients !

Morphy Richards support tells me to tweak the recipe putting less yeast, more water...etc...
I've tried that, did not work much.
Final answer they gave was to press start/stop for 15 sec until hearing a beep to re-set the machine. Or put vitamin C on the bread.

Pressed 15sec, 30sec and 1min...no beeps come from it. Only the machine starts to run.

Does this function really exists or is it just a hoax to keep me searching the fault on my side ?

Has anyone had this type of problem with a Breadmaker ?

Thank you.