After upgrading to Domino 9.0.1 you may run into weird view problems where documents, especially response documents may not appear in categorised views.
Only “shift + F9″ will solve the problem temporarily, but as soon as documents are added to the database, the problem might occur again.
According to IBM Support, this issue has the highest severity and they are working on a fix. It’s supposed to be addressed in FP2 for Domino 9.0.1.
As a temporary workaround, IBM Support recommends to set MAX_PERMUTE_RECURSE=100000 in the server’s notes.ini.
This parameter which is new in Domino 9.0.1 and 8.5.3 FP6 has been introduced due to SPR #KHAN87ZUTS and seems to be part of the root cause because
“…the number of hierarchical responses that can be added to a given collection…”
is now somehow limited.