I tried to buy the LE on launch day, and couldn’t get through the payment page. When it was listed as sold out, I bought a regular deck without much difficulty.
Then I saw the LE was available again, and decided to try to buy it again. I was planning to cancel my original order if I could get the LE.
I tried to check out dozens of times over the next 24 hours, but on the final page I kept getting the “something went wrong” error.
About an hour ago, I decided to cancel my original order (you can do this by requesting a refund on the order page). The refund was issued 15 minutes later.
I went back and tried to order the LE again, 30 minutes after the refund was confirmed. Went through on the very first try.
So from my limited experience, I think Steam might be blocking all LE orders (and maybe even regular deck orders?) if you already have an active order.