That is very common to have short period of an arrhythmia and then you see the doc and you are back in rhythm. The Kardia will record the event in real time. I am assuming you can feel it with it happens. Then you can send the pdf to the doc and they can see read the pdf that you send them. That way you are not playing wack a mole with running to urgent care or the ER and it is already back in rhythm. What kind of doctor are you seeing that is "at a loss" for what causes it? It is caused my any number of issues within the the heart. Some people have "triggers" that they feel starts the event but others do not necessarily notice any triggers.
A good cardiologist who specializes in electrophysiology of the heart is trained to find and understand the underlining mechanisms of what actually is causing the particular arrhythmia you have. There may be triggers that make people feel make it easier to identify but they as still prone to having Afib whether they can identify a trigger or not. Normal hearts do not go into Afib.