It is almost certainly dark type on a transparent background, which vanishes on a dark page. Choose Fix dark mode here in the toolbar while looking at your site, click the logo, choose Use a dark version and pick a light version from your Media Library. Or go to Images and Elements → Image Replacement, and under Dark logo pick it there. It replaces your site logo whenever dark mode is on, in every darkening method, and it is in the page before the first paint — so nobody sees your usual logo flash there first.
If the image that disappears is not your site logo — a badge, a partner strip — use Other image pairs on the same screen, one pair per line:
https://example.com/wp-content/uploads/badge.png|https://example.com/wp-content/uploads/badge-white.pngStill stuck? Ask the developers who wrote it. We aim to reply within one business day.
