Hey there! I'm sorry to hear that you have experienced this issue with your Theonite. We're aware of an ongoing visual bug that makes it so your total Theonite is displayed at an amount that's higher than it should be. Since this is just a graphical error, this Theonite cannot be spent.
Whenever any purchase is attempted in Skullgirls Mobile, the game will perform a check for your connection to the server. Since the extra bugged Theonite does not exist in our servers, this connection check restores your Theonite count to what it actually should be.
After an investigation into your account history I found that this was the case. All your Theonite gains and expenditures carried through at consistent amounts. However, due to this error, when you gained the 50 Theonite from your subscription it added an extra 50 on top that didn't actually exist. When you tried to purchase a relic it then refreshed back to the true amount. I understand this bug may be frustrating, but we are investigating it and will hopefully resolve it as soon as possible!