The Financial Ombudsman Service (Fos) estimates it has received about 20 complaints related to issues surrounding Aviva's re-platforming to date.
The figure is an estimate based on informal record keeping by internal ombudsman teams as the body does not at this stage formally record claims.
A spokesman for Aviva suggested the ombudsman's estimate for the number of complaints it has received about replatforming were not in line with its own records.
A spokesperson for the provider said: "We would not comment on specific ongoing complaints.
"We support the Fos service. We aim to resolve customer cases but where this doesn’t prove possible, the Fos provides an important independent service."
It is unclear what exactly the complaints relate to but Aviva for Advisers has suffered a raft of problems since moving to FNZ technology in January.
A number of advisers FTAdviser spoke to complained about problems allocating their clients' money, as well as issues with processing adviser pay and drawdown payments.
There have also been problems switching funds, facilitating Isa contributions and erroneous alerts sent out indicating huge value drops in client portfolios, all contributing to threaten the adviser-client relationship.
A spokesman for Aviva said it was working to fix the issue as quickly as possible and has pledged it would compensate clients for any losses incurred because of the technical glitches.
Scott Gallacher, chartered financial planner at Rowley Turton, believes people have been flocking to the ombudsman out of frustration with Aviva's inability to stop the ongoing problems.
Mr Gallacher only has a handful of clients with Aviva but said he is facing similar problems with the Aegon-Cofunds migration.
He said he would be surprised if people did not bring claims to the Financial Ombudsman Service, which could end up costing the provider.
Fos charges businesses a case fee of £550 for every claim handled by its case-handling staff or ombudsmen after the first 25 cases, which are free.
Mr Gallacher said: "I would be interested to see what the complaints are about. I am assuming part will just be frustration with the provider. It would just be sheer annoyance.
"That has got to cost them quite a bit and I suspect the number to be growing rapidly. Because initially they would have given them the benefit of doubt but as it goes on and on people will start saying enough."
Mr Gallacher has already issued official complaints with Aegon for the platform's failure to process Isa applications and withdrawal requests within a 'reasonable' timeframe.
Aegon moved more than 400,000 Cofunds users and £37bn of assets across to the Aegon platform on the May Day Bank Holiday weekend and users have been blighted by problems since.
Aegon told FTAdviser this week (7 June) that due to significant demand for the fund supermarket there has been an impact on internal processing times that meant timescales detailed in service agreements were not being met.
But Mr Gallacher questioned this rationale.
He said: "I would be amazed if more people were using the platform after the changes than before. I imagine it is the same number."
He said he has already started to divert client money that would have flown onto the Aegon-Cofunds platform to other providers and started transferring clients away.
As a longstanding client of Cofunds, he said he has lost confidence in the provider's ability to get on top of its problems.
Aviva said: "We are resolving complaints as quickly as possible. We are committed to ensuring that no-one will be financially disadvantaged by our recent platform issues."
carmen.reichman@ft.com
