Why is this hadith classed as Dai'f?

Question

The hadith:

Narrated 'Abdullah bin Mas'ud (May Allah be pleased with him):

The Messenger of Allah (ﷺ) said:

"Indeed the Shaitan has an effect on the son of Adam, and the angel also has en effect. As for the Shaitan, it is by threatening evil repercussions and rejecting the truth. As for the effect of the angel, it is by his promise of a good end and believing in the truth. Whoever finds that, let him know that it is from Allah, and let him praise Allah for it. Whoever finds the other then let him seek refuge with Allah from the Shaitan (the outcast) then recite:

Shaitan threatens you with poverty and orders you to commit Fahisha (2:268)."

^{— Reference:
Jami' at-Tirmidhi
English reference : Vol. 5, Book 44, Hadith 2988 Arabic reference : Book 47, Hadith 3256}

View of Imam Tirmidhi:

Imam Tirmidhi said:

هَذَا حَدِيثٌ حَسَنٌ غَرِيبٌ وَهُوَ حَدِيثُ أَبِي الأَحْوَصِ لاَ نَعْلَمُهُ مَرْفُوعًا إِلاَّ مِنْ حَدِيثِ أَبِي الأَحْوَصِ ‏.‏

Translation (from an English PDF copy):

This Hadith is Hasan Sahih (this word (Sahih) is absent in the text) Gharib. It is a narration of Abü Al-Ahwas, we do not know of it being Marfu' except through the narration of Abū Al-Ahwas.

^{— After narrating the hadith}

So it seems that this Marfoo' hadith is only found through the narration of Abū Al-Ahwas.

View of other Muhaddith:

This hadith is classed as Dai'f by
Darussalam - Hafiz Zubair 'Ali Za'i (May have mercy on him), also by Albani (May have mercy on him) in his book-
Mishkat (المشكاة), 74 and
Dai'f al-Jami' al-Sagher (ضعيف الجامع الصغير), 1963.

And I've noticed that some take this hadith as evidence for the concept of the number of angel with each person being 5 and the 5th one whispering goods into the ear, but many scholars deny this concept.

For example:

Ismail Ibn Kathir (May have mercy on him) said:

There are two angels, one to the right and one to the left of each person, recording the deeds. The angel to the right records the good deeds, while the angel to the left records the evil deeds. There are also two angels that guard and protect each person, one from the back and one from in front. Therefore, there are four angels that surround each person by day and they are replaced by four others at night, two scribes and two guards.

^{— Tafsir Ibn Kathir of Surah Raa'd (13) : 11}

This view is also favoured by Islam Q&A website. Maybe the hadith is Dai'f that's why, this concept is rejected.

The Problem:

But I couldn't find the reason for this hadith being Dai'f in those links of the books.
In fact, there must be any reason for classifying this hadith as Dai'f.
There may be any untrustworthy or unknown narrator or any gap in the chain of narrators or any other reason.
But I couldn't find it.

And through the view of Imam Tirmidhi, it's not clear that for Abul Ahwas, the hadith is dai'f, nor did Imam Tirmidhi directly say it. So it is not possible to be certain.

So I want to be clear on this topic.

And I would like to know why this hadith is classed as Dai'f.

I hope that someone will be able to answer my question.

Jazzak Allah Khair.