There is a known Chrome bug with WP 4.3 that makes the admin menus to get jumbled and sometimes they simply disappear! This problem seems to be targeting Chrome versions 45 and above.
There is a fix that is working out for most people:
- Go to chrome://flags/#disable-slimming-paint
- Enable the “Disable slimming paint” option.
- Ensure that the “Enable slimming paint” option below it is not turned on.
- Relaunch Chrome.
This fix was provided by Samuel Wood (Otto). Thanks.
That worked out for you? Let me know in the comments box.