Is this a recently restored character you are seeing the issue with?
I have had odd issues now and then on restored characters being in the guild, but not in the guild. They can access Guild Bank. But they cannot use Guild Repair. I cannot remove them from guild to reinvite them, etc. The fix I usually see is I wait a day or three and the servers seem to catch up. This usually means the character ends up not in the guild (cause they were deleted) and I reinvite. But not always. Sometimes they stay in the guild.
For instance, I restored Ronalvandy today. He can access the Guild bank. He cannot use the guild repair, it returns Internal Guild Error. If I wait a day or three, he will probably be guildless and I can reinvite him and it is back to normal. The delete process is a bit finiccky sometimes for my guys. Also, I cannot /guit or remove him via the guild settings. But, as I said, in a day or three, he will be guildless and I can reinvite. He is in effect, in the guild, but not in the guild atm.
Maybe you are seeing something similar. Has your attempts been over a few days? If not, perhaps wait a bit and try again?