“Why do I have lapses in hearing?”

Well, you're probably not having lapses. You probably have hearing loss and depending on the degree and pattern, it may affect you more in certain circumstances than others (i.e. background noise, group conversation, rapid speech, soft spoken people, people who do not enunciate, etc). I'd suggest a baseline hearing exam if you haven't had one recently. It's very common to start to noticing some hearing difficulties in your 50s and 60s.