ezic_zone:next/3 was not filtering the Zones to only those after UTCFrom. This may have caused an endless loop, always returning the earliest zone regardless of the progress of time. I wont know; I caught it rather early.
Time comparisons are patently wrong. They do not consider s/w/u/g/z time modifiers, so the comparisons can be off by hours. At least 24 hours within any time or zone change, ezic will give unreliable results.
I think a solution can involve "flattening" the data, starting from the earliest time possible for each zone/rule, going forward.
There exist ambiguous local times for zones and rules. For example, on Nov 7th, in Los Angeles, the times from 1:00:00am to 1:59:59am were repeated, once for PDT and once for PST. Given a local time in that zone between those times, we cannot determine what UTC time is unambiguously. Similar for Zone transitions where fall-back occurs.
