I created my own set of svg files.
Some work as expected. Some, when dragged into Gliffy, either directly or into a custom library, are distorted. The aspect ratio is changed. It looks thinner and taller than the original.
Here is the content of the svg file:
<?xml version="1.0" encoding="UTF-8"?><svg id="Layer_1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 51.56 68"><defs><style>.cls-1,.cls-2{fill:#fffdf1;}.cls-3{fill:#b1191f;}.cls-2{font-family:Verdana-Bold, Verdana;font-size:40px;font-weight:700;}</style></defs><text class="cls-2" transform="translate(38.51 -8.28)"><tspan x="0" y="0">X</tspan></text><ellipse class="cls-3" cx="25.78" cy="7.53" rx="25.67" ry="7.39"/><path class="cls-3" d="m25.46,27.74c14.9,0,21.02-2.25,25.99-6.15v-9.97c-1.47,1.04-3.44,1.98-5.89,2.78-5.31,1.75-12.33,2.71-19.79,2.71s-14.48-.96-19.79-2.71c-2.44-.81-4.41-1.74-5.89-2.78v10.41c4.07,2.79,11.6,5.71,25.35,5.71Z"/><path class="cls-3" d="m25.46,29.74c-13.06,0-20.81-2.6-25.35-5.33v35.41c3.75,3.77,11.19,8.03,25.67,8.03s20.79-2.93,25.67-8.02V24.07c-5.95,4.15-13.14,5.67-25.99,5.67Z"/><path class="cls-1" d="m40.66,63.18h-8.68l-6.26-9.55-6.38,9.55h-8.29l10.31-14.65-10.1-14.43h8.66l6.05,9.05,6.22-9.05h8.31l-10.15,14.13,10.3,14.96Z"/></svg>