I suppose it’s due to imprecise location. Making the area way bigger would solve this at virtually no cost - unless you have something to do at neighbor’s apartment that you want to count as leaving the house.
I’ve heard there’s also an option to set aggregation method to ‘max’. If your ifttt submits a one on each trigger then this would leave not-leaving-house days as they are and turn left-house-multiple-times days into left-house-once days. However, I couldn’t find this in goal settings, so maybe this feature is too premium for my plan.
As for debugging, you would probably want to start with ifttt logs and ‘data’ tab on goal’s page to check timings, down to a second. Did the applet run 4 times in one second, or was it spread out over an hour? If it’s the latter then that’s definitely due to imprecise location. Did the number of applet runs match the number of datapoints?