The phrase "a subject of controversial" is not correct in English.
The correct form would be "a subject of controversy" or "a controversial subject."
Example: "Climate change is a subject of controversy that sparks heated debates among scientists and policymakers."
Alternatives: "a contentious issue" or "a debated topic."
The mechanism causing the instability is, however, still a subject of controversial discussion.
The health safety of aluminium intake has long been a subject of controversial debate.
Whether a coach dismissal during the mid-season has an impact on the subsequent team performance has long been a subject of controversial scientific discussion.
However, further studies are needed to assess the actual ability of AFiPSCs to restore telomere restriction fragment length to an ESC level, a subject of controversial discussion in the iPSC field [45], [56], [57].
Not surprisingly, whether mid-season coach dismissals have effects on the subsequent team performance has long been a subject of controversial discussions, mainly in the Sport Sciences [4] and Economic Sciences as well [1], [5].
Therefore, the expression of cell cycle markers in the adult brain has always been a subject of controversial debate.
Nakata, whose bright performances for Japan at France 98 were almost as conspicuous as his dyed red hair, signed a five-year contract with Perugia in 1998 but soon afterwards became the subject of controversial speculation about a move to Manchester United.
Currently the subject of controversial debates, a statement about the cost-benefit analysis of the e-Prescription is difficult.
Malia and her sister Sasha, 13, were recently the subject of controversial comments about their clothes by a Republican official at Thanksgiving.
The Rocketdyne facility was the site of a partial nuclear meltdown nearly sixty years ago and the subject of controversial and stalled cleanup efforts for decades.
Despite the rarity of recourse to this claim, and despite the emphasis given to the authority of the bishops in the second Vatican Council (1962 65), the doctrine remained a major obstacle to ecumenical endeavours in the late 20th century and was the subject of controversial discussion even among Roman Catholic theologians.
