How do I stop quietly serious issues from slipping down my queue?

You handle the obvious fires well. The trouble is the quiet issue, the one not shouting, that turns out to matter more than the loud ones, and it keeps sliding down your list because nothing about it demands attention. That is a real blind spot, and it is built into how urgency grabs us, not a flaw in your care. Loud and important are not the same thing, but our attention treats them as if they are. The fix is to judge tickets by impact, not by volume, so you deliberately ask of the quiet ones, who does this affect and how badly if it grows? A calm report about a slow leak can outrank ten angry ones about a spilled cup. Making that question a habit is how the quietly serious stops slipping past. Once a day, scan the bottom of your queue on purpose, the stuff that has been sitting, and ask if anything there is quietly bigger than it looks. Just that one deliberate look catches the sleepers that noise would otherwise bury. You already handle the fires. This is teaching yourself to also see the smoke.