[SSSD] Group name lost randomly

[Qing Chang]

at the same time on different IPA clients, group name could become
unavailable on one but not the other:

===== available on fisher =====
fisher:$ groups chuck
chuck : mri hcgrp ccgrp prgrp chuksh crdsh2 ipausers slcc
=====

===== unavailable on robin =====
[root@robin ~]# groups chuck
chuck : groups: cannot find name for group ID 422
422 ipausers prgrp crdsh2 slcc chuksh hcgrp ccgrp
=====

Note in this case 422 is mri, but it could happen to another
GID.

Just did a  "\rm /var/lib/sss/db/cache_sri.utoronto.ca.ldb"
and "service sssd restart", the group name still did not
come back.  A reboot would fix the problem, but it could
creep back some time later.

Any idea why this is happening?

Best Regards,
Qing