Just like title said, all icons in Timeline disappeared. I must guess where the specific button is located. It is very annoying!
Please file a bug report. This is not one that we are aware of.
By using the bug reporter, it should take all of 5 minutes, and the bug reporter will give us all the information we need to diagnose this.
After I delete obj and Library folders and re-open the project everything’s back! I think it may be caused by cache error, but I don’t know how to reproduce it.
Ok, thanks for the heads-up anyway.
any updates on this? I have the exactly same problem, after Unity crashed while using Timeline.
Deleted the “Library” folder inside the project but nothing changed 
. I didn’t had an obj folder
In my case, I do random changes in any script (like adding a space in any line) and let the Editor recompile, and then it was fixed.
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wow, that actually worked! Many many thanks, I was beginning to get crazy over this!
Thanks again!
In the bottom right corner there is a bug icon, you can use it to quickly force the recompile process by switching release/debug modes back and forth.
Unity 2022.3