Perhaps a date range with wrong dates? Sorry, I can not tell it from a screenshot.

It's the custom CSS you've added. It should never refer to a class ".active", as the skin is using that. I don't know what this .crcollapsible does, but you can fix it by using better CSS hooks:

.crcollapsible {
    background-color: #777573;
    color: white;
    cursor: pointer;
    padding: 18px;
    width: 100%;
    border: none;
    text-align: left;
    outline: none;
    font-size: 15px;
	margin-bottom: 0.5em;
}
.crcollapsible.active, .crcollapsible:hover {
    background-color: #555351;
}
.crcollapsible:after {
    content: '\002B';
    color: white;
    font-weight: bold;
    float: right;
    margin-left: 5px;
}
.crcollapsible.active:after {
    content: "\2212";
}
.crcontent {
    padding: 0 18px;
    margin-bottom: 0.5em;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.2s ease-out;
    background-color: #e8e7e6;
}