In V14.2 (or thereabouts), there was also a limit of the number of users which can be added to a JasperSoft role, at least using a Oracle database. This was due to JasperSoft using 'in' statement where Oracle has the limit, which I believe is around 1,000 (we have more than that number of users in Clarity, so it was failing).
Don't know if has been resolved in later versions of Clarity as we gave up using 'custom roles' in JasperSoft due to this limitation.
At that time, it was a matter of selecting the 'first person', scroll down the list, hold down the shift-key and select the last person, painful, and then I hit the above challenge.