Due to a known chrome issue, other extensions such as LastPass can interfere with axe DevTools Extension functionality. As a temporary workaround, you can disable all other extensions which interfere.
Cross-domain iframes have limited support. Limitations include:
selecting elements within cross-domain iframes
running IGTs within cross-domain iframes
Using the keyboard shortcuts can result in display of the old UI (issue #2990)
Some keyboard shortcuts no longer work (issue #2991)