I've tried your code, and the buttons just appear for me, and nothing dissappears. With your buttons included I have 14 buttons, so the limit, if any, sits above that.
In terms of priority, you included priority for your Journal: Today button, that is the way to go. You can also use decimal values, so 2.1 also works.
Hi, did you try the latest stable version of both browsers to see if it's some kind of known issue that has been fixed already? You should mention the browser versions + OS version you are using.
This doesn't sound like a version issue. Maybe something failed during indexing. You can try to run the Space: Reindex command and when that's done reload to see if it helps. If not, have a look at the browser's JavaScript console to see if you can find any obvious errors there.