How is your CSS loaded? i checked your code and for me both names work as expected since both names have the same style definition. Make sure your HTML code is correctly defined with all tags and try refreshing / reopening the program after you changed the id (+saved it).
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
<style>
#myTest {
font-family: "FuzzyRegular";
font-size: 3vw;
overflow-wrap: break-word;
word-wrap: break-word;
color: #000;
text-align: left;
font-weight:400;
letter-spacing:2px;
padding-right: 2.19em;
border-bottom: 5px solid rgba(255, 240, 0, 0.5);
}
#cucamonga {
font-family: "FuzzyRegular";
font-size: 3vw;
overflow-wrap: break-word;
word-wrap: break-word;
color: #000;
text-align: left;
font-weight:400;
letter-spacing:2px;
padding-right: 2.19em;
border-bottom: 5px solid rgba(255, 240, 0, 0.5);
}
</style>
</head>
<body>
<table>
<thead>
<tr>
<td>
<div id="cucamonga">TEST</div>
</td>
</tr>
</thead>
</table>
</body>
</html>