As of 2.6.0 some code was removed from UserInstance which set the "userName" parameter for the theme stylesheet (= person.getFullName()). From what I can see in the change logs, the changes were made to "remove ALM dependencies" from UserInstance. However, no code appears to have been added to the ALM to supply the userName parameter, even though the ALM theme stylesheet (integratedModes.xsl) is still expecting it. The issue appears to have been brought up previously (UP-1478) for v2.4.4.

There IS code in SimpleLayoutManager to set userName, and also in DistributedLayoutManager (according to UP-1397 ... although I don't see it in the 2.6.0 version). But it looks like there is nothing in AggregatedLayoutManager.