Ring alarm armed while door is ajar

It is the second time we find one of our doors having been ajar while system was armed in home mode and us or the system not being aware of it. The most event being about half an hour ago. Checked doors because one of us thought we heard noises. We use “smart” Schlage locks on both entries. So that particular lock must not have been locked, since at that door position could not be (door mostly closed but for a quarter of an inch away from clicking shut. So my dismayed question is: how can my ring alarm have armed in Home mode when my door sensor should have read as open? How can I prevent this from happening in the future? I.e., I want to be made aware of door not being properly locked as I arm the alarm. I definitely do not have peace of mind at the moment.