I redeemed a SubQ Invitation, but cannot access the shop. The invitation is gone from my inventory but the shop is still closed for me.

Is there some kind of limit as to how often you can visit the SubQ? I did redeem an invite earlier.

Check the other currencies in your vault to make sure that it did for sure get redeemed.
If it doesn't show up as being redeemed do an account search to make sure it didn't accidentally get put in a shop or a treasure chest. If those two look fine, make sure you are using the New Subeautique Link to access the shop. The old one is no longer of any use. If none of those solve your issue, you should probably File a Ticket Hope you find what happened to it!

Actually I was wondering about the same thing the other day. I thought I had two invites left.. bought one thing and suddenly no invites. :/