Glossary entry (derived from question below)
English term or phrase:
non-billable rework
Arabic translation:
تكرار العمل دون عائد/ تكرار العمل بدون مقابل
English term
Germany
professional and timely manner
Native in: Arabic (Variants: Tunisian, Iraqi, Sudanese, Egyptian, Lebanese, Palestinian, Yemeni, Saudi , UAE, Standard-Arabian (MSA), Moroccan, Syrian, Libyan, Kuwaiti, Algerian, Jordanian) 
Works in: English to Arabic, German to Arabic, Arabic
non-billable rework
إعادة عمل غير قابل للفوترة؟
Or would you have more creative suggestions?
Proposed translations
Morocco
Literature,Marketing & Legal Translation
Native in: Arabic (Variants: Moroccan, UAE, Kuwaiti, Najdi, Standard-Arabian (MSA), Hassaniya) , Berber (Other) (Variants: Standard Moroccan Tamazight, Tarifit , Tashelhit , Riffian, Central Atlas Tamazight, Tamazight ) 
Works in: English to Arabic, French to Arabic, Arabic to English, and 21 more.
تكرار العمل بدون مقابل
بدون أجر
Rework is not clear here since there is not enough context. It might be translated into
تكرار العمل
تكرار الشرح لأن النص يتحدث عن مشاكل التواصل
https://context.reverso.net/translation/english-arabic/non-b...
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Note added at 14 mins (2021-07-26 18:39:02 GMT)
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Non-billable (NB) is a term we use to describe time spent on work that we will not be reimbursed for.
https://www.google.com/search?ie=UTF-8&client=ms-android-sam...
France
Arabic professional content & beyond...
Native in: Arabic (Variant: Standard-Arabian (MSA)) , French (Variant: Standard-France)
Works in: English to Arabic, French to Arabic, German to Arabic, and 6 more.
عمل إضافي دون عائد
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Note added at 13 mins (2021-07-26 18:37:58 GMT)
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عمل إضافي دون عائد مادي
28 years of experience
Native in: Arabic (Variants: Iraqi, Sudanese, Egyptian, Jordanian, Yemeni, Saudi , UAE, Lebanese, Syrian, Libyan, Kuwaiti, Standard-Arabian (MSA), Palestinian)
Works in: English to Arabic, Arabic to English, Arabic, and 5 more.
أعادة عمل غير قابل للفوترة/إعادة عمل غير محسوب
إعادة عمل غير قابل للاحتساب
إعادة عمل غير قابل لتحرير فواتير عليه
إعادة العمل (من جديد) بدون اجر
أعادة عمل بدون تحصيل اجر عليه
إعادة عمل بدون فوترة/بدون تحرير فواتير
قابل لتحرير الفواتير/فوترة
https://www.almaany.com/ar/dict/ar-en/billable/
Morocco
Juggling languages: a science and an art
Native in: Arabic (Variants: Moroccan, Standard-Arabian (MSA)) , French
Works in: English to Arabic, French to Arabic, Arabic to English, and 3 more.
هدر مجاني للمداخيل بسبب العمل المعاد
تكرار القيام بالعمل بدون مقابل مادي
روتيني لا يستغرق وقت مهم مما لا يستوجب الدفع
Passionate Interpreter | Language Adorer
Native in: Arabic
Works in: English to Arabic, Arabic to English, Arabic, and 1 more.
مهام مكررة ( /تكرار المهام) من غير أجر ( /بالمجان)
Suggested Translation Into Arabic
1= مهام مكررة من غير أجر
2= تكرار المهام بالمجان
As the idea seems to be:
It refers to a certain work, which is not don't appropriately, thus, it must be done again.
BUT, as long it's not the client responsibility by any means, then it's done for free.
P.S.: the examples in the links below clear the idea I am trying to express in my brief explanation (to what I have perceived from the question).
هدر الوقت والجهد
ضياع الوقت والجهد = عمل بدون مقابل
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