Those in service go on reacting strangely (12)

I believe the answer is:

congregation

I'm a little stuck... Click here to teach me more about this clue!

'those in service' is the definition.
The definition suggests an adverb but the answer is not.

'go on reacting strangely' is the wordplay.
'strangely' indicates anagramming the letters.
'go'+'on'+'reacting'='goonreacting'
'goonreacting' anagrammed gives 'CONGREGATION'.

Can you help me to learn more?

(Other definitions for congregation that I've seen before include "Group assembling for worship" , "Group of worshippers" .)

I've seen this clue in The Telegraph and The Globe and Mail.

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