fragmented sysauth$ table

we are on Oracle 19.8. customer has several large databases, with several tens of thousands users and a number of roles.  

We are experiencing slow "set role" (15 seconds and up), and we see some "select . from sysauth$" in top10 SQL of the AWR Reports . I can see that sys.sysauth$ is fragmented, 40% wasted space in there.  

Is there a way to compact this table? Alter table move or similar do not work on it.