I've recently found that Epiphany uses its own compose sequences instead of the system-wide ones - e.g. dead_acute + dead_acute produces an acute accent on every other app, but nothing in Epiphany.
This also affects sequences using the compose key.
This still appears to be an issue.
Yes, it's sad that after almost two years no one has bothered to even confirm this bug
That's my fault in the end, but rest assured I plan to fix it soon.
Fixed by https://bugs.webkit.org/show_bug.cgi?id=84556