Okay, ran some tests - 100 revives later and found no issues there, no instances where it skipped for me.
The tests were run against monster damage. At this stage, can only assume there's a trigger elsewhere that's causing it - possibly a map condition causing it? or player vs player damage causing it? From the comments in this post, it all seems centered around PvP combat as opposed to monster combat.
Anyone noticed any particular patterns? I.e. have these instances only ever occurred on particular maps / against certain targets (monsters/players/map damage events) / at certain intervals (i.e. within [x] timeframe since previous login)?
OR (probably a long shot but) after being hit by certain spells/abilities?