Nissan GT-R R35 PR has stopped increasing

My Nissan GTR has reached a point where the PR no longer goes up.  I recently upgraded several epic parts from 5 Star to 6 Star (30 points increase per part) and my PR has not moved from 766 which means I am unable to complete the Ichi Nissan or Super Coupes car series as both require a PR higher than 766.

I note that I am not the first person to have an issue with their car PR not increasing - when will a bug fix be released for this issue?