Black Market SDU Upgrades Listed as "Sold Out"

After purchasing the last two backup upgrades I am stuck at 33 backpack slots. When I go to the black market the upgrade shows as “Sold Out”, so the game has clearly registered the purchase, but I didn’t actually receive the last two upgrades.

There was a glitch with the last two slots disappearing, and taking whatever was in them too. See this thread for more details. Hopefully, you should get the slots back in a future update without having to re-purchase them. See also this post.