In an update on 19 July, APJ said that number has risen to 210.
The scheme, InvestUS, purchased repossessed properties in Detroit, Chicago and Florida that had been foreclosed after the financial crisis.
The properties were renovated, let and sold on, with investors promised returns of 15% per year over three years.
The firm said the clients “could be due millions in compensation following the failure of the scheme after they were misled about its suitability as a pension investment”.
The largest loss reported by an individual client is £80,000, although many have lost significantly more after also investing in other failed schemes including Ethical Forestry and Global Plantations.
APJ originally estimated that clients could collectively be due £7.3m ($9.5m, €8.2m), but offered no update on this figure in the recent statement.
How it worked
APJ clients who invested into InvestUS held their pensions in Sipps with under-fire providers Liberty Sipp and Guinness Mahon.
The firm has already issued legal cases against both providers for allowing Sipp investments into a range of unsuitable schemes including Ethical Forestry and Global Plantations.
It also alleges the pension transfers were made on the advice of Avacade, an unregulated introducer which conducted free pension reviews and promised individuals far greater returns than their DB pensions offered.
In order to fast track these investments, Avacade enlisted independent financial adviser Shah Wealth Management to carry out risk reports on the suitability of the investments on a one-off basis.
Both Avacade and Shah Wealth have since been liquidated.
Glyn Taylor, solicitor at APJ, said: “We have recently seen huge growth in the number of clients contacting us about investments into InvestUS. Our clients were unaware of the risks involved in the scheme and as a result have lost their life savings.
“Had they known the high-risk, non-standard nature of InvestUS, they would not have invested in the scheme.”
Taylor added: “Due to the involvement of the regulated party, which has now been liquidated, we can seek redress for these clients from the FSCS and we’re confident we will be able to secure fair compensation for their losses.
“However, many of the clients who have now come to us, also invested into other schemes as part of the Sipp schemes. These schemes have also failed and, as there wasn’t an IFA involved, clients can’t seek compensation from the FSCS.
“To ensure clients get full compensation for all their losses we will also be litigating against their Sipp providers to secure compensation for these additional investments.”