The threat posed by ISIS was "mostly high in conflict zones and low in non-conflict areas" during the first half of the year, the experts said in the report, circulated on Monday.
The panel said in the report presented to the UN Security Council that "the overall situation is dynamic".
Despite significant losses in the group's leadership and reduced activity in Syria and Iraq, the risk of a resurgence remains, the experts said.
“The group has adapted its strategy, embedding itself with local populations and has exercised caution in choosing battles that are likely to result in limited losses, while rebuilding and recruiting from camps in the north-east of the Syrian Arab Republic and from vulnerable communities, including in neighbouring countries,” they said.
In 2014, ISIS declared a self-styled caliphate in large parts of Syria and Iraq.
The group was defeated in Iraq in 2017 after a three-year battle that left tens of thousands of people dead and cities in ruins. But ISIS still has cells in Iraq and Syria.
Despite sustained counter-terrorism operations, ISIS has between 5,000 and 7,000 members, mostly fighters, across those countries, the experts said.
But they said the group reduced its attacks deliberately “to facilitate recruiting and reorganisation".
In north-eastern Syria, about 11,000 suspected ISIS fighters are being held at sites controlled by the Kurdish-led Syrian Democratic Forces, which played a prominent role in the fight against the terror group, the panel said.
The fighters include more than 3,500 Iraqi citizens and about 2,000 from almost 70 countries, it said.
North-east Syria is also home to two closed camps, Al Hol and Roj, where about 55,000 people with alleged links or family ties to ISIS live in dire conditions and "significant humanitarian hardship", the experts said.
About two thirds of the population of the camps are children. They include about 11,800 Iraqis, nearly 16,000 Syrians and more than 6,700 children from about 60 other countries, the experts said.
The panel quoted one unnamed country as saying ISIS maintained its “cubs of the caliphate” programme, recruiting children in the overcrowded Al Hol camp.
In addition, more than 850 boys, some as young as 10, were in detention and rehabilitation centres in the north-east, the experts said.
UN members have assessed that ISIS pose the most serious terrorist threat in Afghanistan and the wider region, the panel said.
The terrorist group has reportedly increased its operational capabilities and has between 4,000 and 6,000 fighters and family members in Afghanistan, it said.
But the experts said operations involving regional forces in Mozambique’s Cabo Delgado province disrupted the activities of a group affiliated to ISIS.
Countries in southern Africa estimate the group now has between 180 and 220 male fighters with battlefield experience, down from 280.
Several countries in the east of the continent have expressed concerns that terrorist groups, including ISIS, could exploit political violence and instability in Sudan the experts said.
Some countries have said the ISIS affiliate in the Sahel region “has become increasingly autonomous and played a significant role in the escalation of violence in the region, alongside other terrorist groups", the UN panel said, referring to increased ISIS attacks in Mali, Burkina Faso and Niger.