This issue is strange when it comes to reproducing it, since it doesn't affect all users the same way. It's reproducible on both Mac using Firefox and Windows, using both Firefox and Chrome. The steps to reproduce this issue are as it follows (on demo-author):

1. Use Firefox/Chrome
2. log in as superuser
3. add new page (basic template)
4. add image component
5. now switch to the asset app
6. edit asset you used in the image component and upload a diffrent picture
7. switch back to the new page -> old image is still there (see: blob:https://jira.magnolia-cms.com/1eaae7d4-2242-4064-bc52-0e79cd378295)

It looks like a possible browser issue, but the fact that it can't be reproduced constantly even using the same browser version on different devices made it a pain to test.