Four

Is there a word or phrase for the sum of many small annoyances, each one viewed by its own being not worth mentioning, that aggregate to a major issue, that itself is hard to pin down?

Death by a thousand cuts seems to violent a metaphor. Wikipedia also knows about the tyranny of small decisions, but that only fits to the degree that the annoyances are actually caused by a decision.

It is not one of the classical system traps according to Meadows (policy resistance, drift to low performance, seeking wrong goals, shifting the burden ot the intervenor, tragedy of commons, success to the successful, rule beating), at least not in their pure form, although a lot of the annoyances can be seen as manifestations of the traps.

Maybe it is a signal of missing feedback loops in the system itself. But, what ever it is, it's not pretty to be in that state.