Try logging into InVision in another browser or in an incognito/private browsing window. If the images load there, clear your cache and cookies, then re-launch your browser.
Re-sync or re-upload your screens. Note: If you've added hotspots or comments to the affected screens, be sure that you do not delete the screens and re-upload. Doing so will cause the hotspots and comments to be lost. Instead, you should leave the screens in place and simply re-sync/re-upload the screens again. If the filenames are the same, they'll be replaced without comments or hotspots being lost.
If the tips above do not resolve your issue, contact us with the name of the affected project and the names of a few of the affected screens, and we'd be glad to help.