This is most likely to be calcium build-up which can be confusing at times:
There are different types of calcium.
The first type is an insulating type calcium, where it just continuously cakes the plates of the OXI cell which will require regular cleaning. To combat this you can adjust the CELL CLEANING hours in the main menu to as low as 4 hours which will reverse the polarity of the OXI cell quicker therefore making it less likely to build up on the plates.
Alternatively, you can also use a calcium softener to try and soften the calcium before it builds up, or try a calcium reducer if levels are too high.
Another contributing factor is high pH however, if you are regularly testing your pool water and controlling the pH this will definitely assist with less build up.
Other types of calcium can build up slightly and when the cell reverses it will knock it off and very rarely build up like the above. The flakes you may see in the pool is totally normal. When the cell reverses it knocks of the calcium (self-cleaning) back into the pool and the pool cleaner (suction or robot cleaner) will pick it up from the bottom of the pool and it will go to the filter and eventually to waste when backwashed.
In the past before self-cleaning technology was around pool owners would have to turn the system off, take the cell out and clean it in an acid and water solution. This is still required in some cases. Inspecting and cleaning the OXI Cell