The CSS is not added by GP so it’s not a bug of GP. If it’s not added by you then it’s added by another plugin.
Here is the full CSS I see being added:
/*
Image Padding Css
*/
.post-image img {
position: relative;
vertical-align: middle
}
.post-image + .entry-header + .entry-content:after,
.post-image + .entry-header + .entry-summary:after {
clear: none;
}
.post-image-aligned-left .site-main .inside-article div.post-image {
margin-top: 10px;
margin-left: -25px;
margin-bottom: 10px;
}
.post-image-aligned-right .site-main .inside-article div.post-image {
margin-top: 10px;
margin-right: -25px;
margin-bottom: 10px;
}
.post-image-aligned-center .site-main .inside-article div.post-image {
margin: 10px -25px 10px -25px;
}
.page-header-image, .page-header-image-single{
margin: 10px -25px 10px -25px;
}
If you didn’t add that, then try #1 on this page:
https://docs.generatepress.com/article/debugging-tips/