Money from my Apple Cash balance suddenly disappears??

My sister sent me exactly $30 to my Apple Cash balance through Apple Pay (iMessage). Afterward, I tried to transfer the cash to my bank, but at first, it wouldn't let me send all the money at once to my bank, which was very strange. I tried sending a lower amount ($20) and it worked. Even more strange, $8.99 completely disappeared from my balance and I only had $1.01 left, so I just transferred the remaining.

I am just so confused about how $8.99 completely is completely lost with no explanation. Especially in a system created by Apple. I can't trust this company anymore.