Ok, I went into an LFR raid and defeated a boss. So, I rolled on the items I needed and lost. So, I return to the same LFR raid on the same day and can not roll for loot. I just returned to the game last week, so I do not know if the LFR loot system has changed. So now I can only roll on gear next week.
You are only eligible for loot from each boss once per week on each difficulty. This has always been the case for raids fro as long as systems have been in place that let you rekill a boss during the week. (You could use the extra roll tokens that were in older expansions on bosses you’d already killed, however.)
What has changed is how the loot is distributed. Instead of personal loot decided if you got something on your kill (and then what it was) now the boss just drops loot that people can roll on. (Someone else might have more info on the rules on what people can roll on.) In theory, it should work out the same. (With personal loot, the game was basically doing the same type of rolls invisibly.) The rolling system does create more friction in LFR, in my opinion, though.
Ok, that make since. Thank you!