wiederkehrend
recurring
Something that happens at certain intervals or again and again; occurring repeatedly.
Er leidet unter wiederkehrenden Albträumen.
He suffers from recurring nightmares.

recurring
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recurring
Something that happens at certain intervals or again and again; occurring repeatedly.
Er leidet unter wiederkehrenden Albträumen.
He suffers from recurring nightmares.

'Wiederkehrend' (recurring) is the present participle of the separable verb 'wiederkehren' (to recur / to return). It is made up of 'wieder' (again) and 'kehren' (to return) and therefore describes something that keeps coming back.
Das wiederkehrende Motiv in dem Roman ist die verlorene Heimat.
The recurring motif in the novel is the lost homeland.
As an adjective, 'wiederkehrend' (recurring) can stand before a noun or be used as part of the predicate at the end of the sentence. Both positions are common.
Das ist ein wiederkehrendes Problem mit der Software.
That is a recurring problem with the software.
The adjective is often used to describe regular or chronic things. Typical combinations are 'wiederkehrende Schmerzen' (recurring pain), 'wiederkehrende Fragen' (recurring questions), or 'wiederkehrende Ereignisse' (recurring events).
Gegen die wiederkehrenden Kopfschmerzen hat sie ein Medikament bekommen.
She was given medication for the recurring headaches.
regular
'regelmäßig' and 'wiederkehrend' both have to do with things that happen more than once. 'regelmäßig' emphasizes fixed or similar intervals, so a clear rhythm. 'wiederkehrend' mainly says that something keeps coming back; the intervals do not have to be exactly the same. 'regelmäßig' often sounds more natural in everyday language when talking about habits or appointments. 'wiederkehrend' fits well with problems, costs, tasks, or events that occur again and again.

Die Firma prüft wiederkehrende Fehler im System besonders genau.
The company examines recurring errors in the system especially carefully.
Auf der Feier rufen die Eltern regelmäßig nach den Kindern.
At the party, the parents regularly call out to the children.