Reproducible Example
Running this example flow.cylc:
[scheduling]
initial cycle point = 20201010
final cycle point = 20201010
[[graph]]
R1 = foo
[runtime]
[[foo]]
script = false
[[[events]]]
failed handlers = echo hello
I look at Edit Runtime in the WUI and see nothing about event handlers in there.

Expected Behaviour
As events is a section within a tasks runtime area, I expected to be able to modify the [runtime][task][events] entries and any defined should be visible.