The £8bn of Nationwide assets managed by Cofunds are yet to be moved to the new Aegon platform.
After acquiring Cofunds, Aegon confirmed it would continue managing assets from Nationwide’s online investment service.
Nationwide has approximately £8bn of assets managed through Cofunds’ investor portfolio service, which Aegon inherited when it bought the platform in 2016.
An Aegon spokesman says a date has not yet been set for when the assets will migrate to the new platform.
Aegon created a clone of its Aegon Retirement Choices platform to move the Cofunds clients onto and will merge the two systems later in the year.
Advisers faced issues following the migration in May, complaining about customer service delays and being locked out of the new system.
Aegon apologised to advisers last month for the disruption and moved 200 employees to its operations team to help deal with further issues.