Looking at the code this is only a UI problem and should not have any impact on functionality of the plugin.
The only thing rolestategy uses from matrix auth plugin is the function doCheckName from the descriptor of GlobalMatrixAuthorizationStrategy. This method is used to decide if the user/group exists and which icon to display.
Locally I copied the relevant code from version 2.6.11 of matrix-auth to rolestrategy and the issue is gone and everything still compiles and works as before.
The question is if we want to also have that separation between users and groups in rolestrategy. If yes that would be some bigger work I think and another question would be if we then want to keep the dependency to matrix auth plugin, probably some part of the code could be reused. After a first peek there are some code parts that are useful that are currently restricted with NoExternalUse