The firm reported gross inflows of £578m in the three months to the end of June, compared with £637m during the previous quarter.
Net inflows dropped from £301m in Q1 to £193m in Q2, though they were up on Q2 last year, when it was £165m.
Despite this, assets under management rose 5 per cent to £18.9bn, from just under £18bn the previous quarter.
David Ferguson, Nucleus' founder and CEO, said he was pleased with the results: "The first quarter of 2021 was incredibly strong for new business activity, and it was pleasing to see inflow momentum continue throughout Q2 and to reach £19bn of AUA following the quarter end.
"It was a particularly resilient performance given the ongoing uncertainty of the takeover process and reflects the ongoing achievements and fortitude of our people along with our commitment to continually improving the core platform proposition for our users."
Following the acquisition of assets from OpenWealth in December, a new Glasgow office was opened in May.
The deal with James Hay's private equity parent company, worth nearly £145m, was agreed by 94 per cent of shareholders on March 30 and will create an entity with a combined £45bn in assets.
However, in February it emerged that Nucleus staff were told there could be redundancies at the firm post-takeover.
In the details of the deal, published to the stock exchange, James Hay said a review of the companies and an integration process was expected to take up to 12 months.
This process could lead to a "moderate reduction" in headcount where there was "duplication or where operational efficiencies could be achieved", the announcement said.
At the time, experts also warned there were “significant challenges” ahead for the merger in terms of technology.
James Hay will merge operations of Nucleus with James Hay Group to create one financial planning and retirement-focused adviser platform.
Although there is no immediate change for advisers on either platform, Nucleus will ultimately be shifted from the Bravura technology it currently uses to FNZ — a platform tech firm with which James Hay has recently secured a long-term strategic partnership.
At the time the deal was announced, Rich Mayor, editorial director at Fundscape, said: “There are significant challenges ahead.
“Nucleus has built a reputation for using data science to enhance its platform services, and worked hard to build a close relationship with Bravura.
“FNZ provides tech to some of the largest platforms in the UK [...] so Nucleus having as close a relationship with FNZ will be challenging.”