If you are showering twice a day, especially with a soap high in oleic acid (which your olive/rice bran soap would be), then the soap will not be drying fully between uses. Once an olive soap has absorbed water, it easily loses mass the next time you wash with it. A simple fix for this would be to rotate your soaps, so that the soap has enough time to dry between uses.
This will not happen to the same extent with a soap made with more of the harder fats and butters, but it is still a good idea to rotate your soaps if you are showing frequently (or multiple people are using the soap).
Customers? This thread is a good resource:
https://www.soapmakingforum.com/threads/are-you-ready-to-sell-your-soap.16002/
Your soap is very young for an olive/rice bran recipe (at the most it can only be 10 weeks old, given that you first made soap in July of this year).
A young soap will not last nearly as long as a well aged soap. This is particularly so for an olive/rice bran soap such as yours; the soap will not last nearly as long as the same soap aged for 8 months or more (soaps high in oleic acid, such as olive/rice bran soaps, need a fairly long cure before they are at their most long-lived).
As a general rule, any soap used before it has been fully cured will dissolve quicker than a well aged soap.
If you want an additive to decrease the solubility of your olive/rice bran soap, you could add a little salt to your water before you add the lye, but it may not be as necessary if you rotate the soaps between uses and age the soap a little more.