The current project began after an inspection in late August found that the tension of 'scarf joint assemblies' linking vertical piers with horizontal beams on the funicular viaduct fell below the designated level.
Engineers have been using specialist equipment throughout September and October to restore tension in the assemblies as well as working alongside the project team to carry out rigorous trials and testing to ensure solutions are effective.
A spokesperson for Highlands and Islands Enterprise said: "Achieving resolution of the tensioning issue has proven more difficult and time-consuming than we had anticipated at the outset. At the same time, though, there can be no short cuts when passenger safety is concerned.
"We apologise to Cairngorm visitors for having to withdraw the service while these works are carried out.
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"We are now looking forward to completing the project during November when the operators of Cairngorm Mountain will also be carrying out their annual maintenance programme.
"Every effort will be made to reintroduce the service in good time for the start of the 2023/24 snowsports season at Cairngorm."
Cairngorm Mountain remains open to visitors, with access available to a wide range of family-friendly activities and facilities in the heart of the national park.
These include the newest addition of a mountain bike park, fun tubing slides for all ages, café, walking trails, a mountain garden, and camera obscura.
Opened in 2001, the funicular was taken out of service in October 2018 following the discovery of structural problems. A £25m reinstatement programme, funded by the Scottish Government and HIE and led by HIE contractor Balfour Beatty, ran from November 2020 until November 2022 and the service was relaunched in January 2023.
The need to restore tension in the joint assemblies was identified during a 12-month 'snagging' programme that had been included in the reinstatement programme to identify and treat any issues that might emerge once the railway was back up and running.
The funicular is a unique and complex structure, comprising a mostly single track and a short loop section where upward and downward trains can pass one another.
The 1.7km viaduct is supported by 94 piers of varying heights, each one effectively a small bridge. It ascends 450 metres up Cairn Gorm, with the track entering a 300m tunnel in its final stage leading into the top station.
Technical challenges involved in the current works are compounded by the mountain location, where access can prove difficult and weather and temperature conditions are prone to sudden and dramatic change.
