I don't believe the coins are meant to show up under the credit transactions. They don't for me. Therefore, to make sure I am getting my coins, I have always checked the number of coins before claiming my 7th day reward. So far I have always gotten the correct amount.
While I was writing this, I noticed that with the LSSM V4 credits expansion, you can see a sperate list of coin transactions (screenshots). All my rewards are shown there, though I haven't been able to find this feature on the base game.
I don't think this thread is a bug.
- On the german version the coins do show up under their own tab called "coin transactions" (under the same UI though)