Fidelity has responded to adviser complaints about the FundsNetwork platform, claiming issues advisers face are minor and it is in the final stages of completing a major upgrade.
A number of advisers have voiced concerns as to the level of service provided by Fidelity, with one adviser claiming he has moved a significant percentage of clients away from Fidelity's FundsNetwork platform as a result of issues left unrectified in recent years.
Fidelity currently operates a system of two separate sites on its platform, one 'classic' and one 'enhanced'.
A Fidelity spokesperson said the older classic site will be shortly decommissioned in the final stages of its technology upgrade, with the "enhanced and upgraded" platform remaining.
Alan Parkinson, managing director at CPD Independent Financial Advisers, said this system has created an "unfathomable" situation for advisers, who must "flip-flop" between the two sites in order to manage a client's portfolio.
He said: "Sometimes funds and numbers are also missing between the two sections, or an investment will be listed as directly invested by the client when in fact it has been done so via an adviser.
"This can lead to great difficulty further down the line when trying to do a valuation and only half of a client's investments are viewable."
Mr Parkinson said Fidelity had admitted a technical fault when he regularly reported the platform's webpage would not scroll down far enough to reveal the entirety of a client's portfolio, but claimed the feedback and support offered by the provider was not satisfactory.
He said: "Over the last 12 months I have been steadily moving clients off the platform and on to others, I could no longer stand the lack of response from Fidelity or poor excuses."
Fidelity declined to comment on the specific issues experienced by Mr Parkinson.
Mr Parkinson said the other platforms he uses are simple and easy to navigate and he does not charge clients for the switch, which he will only consider if a saving can be justified or return matched.
A spokesman at Fidelity International said the the feedback from the majority of advisers who use its upgraded platform has been "overwhelmingly positive".
He said: "While we regularly conduct adviser research and testing before introducing any changes, when completing a project of this magnitude there will inevitably be some minor issues and it is disappointing to hear that a small number of advisers have had a less than satisfactory experience.
"We are committed to a multi-year programme of investment and developing the platform to meet the evolving needs of advisers and their clients and have a number of enhancements planned in 2019.
"These include further improvements to usability and consistency of our transaction journeys across our product range (including Sipp), enhancements to client and income reporting, and additional functionality for firms with discretionary permissions."
Concerns have also been raised as to changes to the layout of Fidelity's website, with suggestions it requires more time and effort from advisers to navigate a newly designed layout.