Plants looked burnt, then died

A question from a fellow grower:

I’m a beginner having recently been given a grow license f for personal use. I was given some seeds of a strain I couldn’t find any information on called lemone, lemon. I started the seeds and through most of the vegetation period they looked great. Then for for no foreseeable reason they started showing signs of being burnt. Within a short time ago six plants died. Morning I could do worked. I’m trying to find out what happened so on my next grow I don’t have a repeat. can you help?

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