Techdisk
TL;DR / Reproduction steps:
  1. Have a VRChat account that has claimed at least one bundle pack.
  2. Create a brand new Steam (or other platform?) account that is eligible to receive and claim the same bundle pack that was already claimed by the VRChat account, and do NOT claim that bundle.
  3. Merge the accounts.
  4. You now have a fully functional merged VRChat account, but it has notifications reminding you to claim packs that you already claimed, and won't let you claim them again. An error appears when you attempt to claim the packs.
4a. Item packs do actually seem to be claimable twice, but you will not actually be able to place two of the same item. The second item just takes up space. Sticker packs cannot be claimed twice and will give an error.
  1. Also it seems like the broken summer sticker pack which can't be claimed still hasn't expired despite it being the 25th today...
Full story:
I recently, and somewhat accidentally, logged in to VRChat using Steam rather than my well-used veteran level VRChat account. Therefore, I decided to merge this brand new account into my existing VRC account so that I could more easily login via the "steam" option (and not have to type my password in VR). That part worked 100% fine and they're merged, but before I merged them the Steam account was given access to the Summer Bundle and starter sticker packs, along with the starter items, which I did NOT claim before merging.
Now, my main, merged VRChat account has persistent notifications reminding me to claim the sticker pack and the summer bundle... which I cannot claim because I already claimed them. I was actually able to claim the starter item pack, leading me to now have two Reference Cubes(tm) in my inventory! Unfortunately (for me, fortunately for you) I can't actually place two cubes at the same time, since they both appear as placed when one is placed. Shame.
Oh, and despite the summer sticker pack expiring yesterday, my broken pack is still there, taunting me....