I have one toon (Flenny - Priest - Korialstrasz) who used to be exalted with the guild but when I tried to use the mobile guild bank, I was notified that this toon’s rep wasn’t high enough. I looked at his rep and it was at 0, neutral. I created this toon back in Wrath and he’s been exalted since back then. He didn’t leave the guild…been in the same guild since Wrath. Not sure when it happened since I don’t try to access the guild bank daily on this toon, but I noticed it today. Tried to submit an in-game report, but it kept pointing me to the forums.
I, too, ran into this same exact issue with one of my toons. He’s been exalted for years. Then all of sudden today, I noticed I was getting rep for guild.
This is a known issue. Is Blizzard ever going to acknowledge this bug? Not just this guild rep bug. But guild items disappear and never reappear.