If images are not showing in the dashboard, that's a common problem, usually caused by "Lazy Loading".
Lazy loading is a feature of performance-oriented plugins such as WP Rocket, WP Smush, and others.
To resolve the issue you would need to exclude the vendor dashboard from lazy loading in those plugins' settings.
An easy way to check if that's the issue is to first deactivate all other site plugins. If that solves it, you can then re-enable site plugins until you identify which plugin specifically causes it.
For example, to resolve it with WP Smush, you can add the "/vendor-dashboard" link to the exclusion list: