Some native keyboard accent shortcuts not working since OS X 10.11.3 Update I have a Qwerty keyboard on my MacBook Pro late-2015, set to the standard US layout, that I sometime use to write French accentuated characters. 

However, since the last OS X update, some accent shortcuts are not working anymore. More specifically, Option6 (+ some vowel), which used to produce circumflex accents now writes §, and Optionc, used for c cedilla, is now used for capitalising the last written word. I can still write these characters using the press and hold method, but it's pretty inefficient.

How can I re-enable these accent shortcuts?
Go to system preferences/keyboard/input sources and make sure that only the item called "US International PC" is on the list, or the item called "ABC Extended" (known as "US Extended" prior to OS X 10.11).

(The standard US layout does not use Option 6 for circumflex, it uses Option i. The US International PC layout uses Shift 6, while ABC Extended uses Option 6. I suspect you were using one of these layouts rather than "US".)