Not sure what is going on. I would put text boxes (temporarily) on the canvas to see what the actual values of A1, B1 and the result of the formula. Seems to be pretty odd behavior.
Have you tried adding the formula cell to your spreadsheet table, to ensure that it is returning 30? That would be my first step, to determine whether it’s a problem with the formula or the alerter.
My second step would be reviewing the properties of the alerter very carefully. Especially if this your first time using them. It’s very easy to do something like apply your rule to the format side and then choose to display bubbles.