This analysis suggests that even though Omicron can be associated with gastrointestinal symptoms, the rates are not higher than previously seen in Delta, and one or more other types of tummy bug are likely to be going around in the population at the current time.
The norovirus for example is an extremely common condition occurring around the same time hence its nickname, the Winter Vomiting Bug.
Unfortunately, there is currently no way of testing whether people reporting gastrointestinal symptoms in the app are infected with the norovirus.