Against certain mobs life blast will show “out of range” when you are actually in range. A couple examples I can think of are Maw and Megadestroyer I was at roughly 600 range and it showed as “out of range” for every hit.
More info in necro subforum here:
https://forum-en.gw2archive.eu/forum/professions/necromancer/BUG-Life-Blast-not-hitting