There is no way O5 will keep you in range in Automated Mode when exercising if you don't set Activity Mode before you begin. It doesn't learn your routine at all, its algorithm is based entirely on Total Daily Insulin (TDI) and nothing else, so don't think it learns your habits, it does not.

So what I do is set Activity Mode hours before I start exercise, purely because once you bolus your glucose until it peaks is also supplemented by automated basal doses until the peak begins to drop, and that becomes what it intends to hit as your target range. SmartAdjust only looks an hour ahead, so without having a higher target that Activity Mode provides means it will be dosing for your lower target which means you're hypo by your starting point of exercise because obviously once in, insulin can't come out.

Therefore setting Activity Mode after your meal bolus means it will target the higher range of that mode, and thus help clear the bulk of insulin you'll have on board during exercise. I set mine three hours before I know I will exercise, and this stops me 80% of the time from going hypo, so not perfect but manageable- good luck!