Did you reindex old log files post upgrade or remove them?
PMTR-60610: R81 includes the new mechanism for log indexing.
Before you upgrade a Management Server or Log Server that uses an external storage device to keep the log data, you must follow the instructions in sk66003 to change the location of the existing log indexes.
This applies only if it is necessary to keep the existing log indexes and use them after the upgrade.
This applies to Security Management Server, Log Server, Multi-Domain Security Management Server, Multi-Domain Log Server, SmartEvent Server, StandAlone Server. R81
GNG-1259,PMTR-52941 R81 includes new logs indexing mechanism, so when upgrading Management server/Log Server/Multi-Domain Server/Multi-Domain Log Server/SmartEvent from R80.x, old log indexes are not upgraded.
The indexing mechanism will re-index the last 24 hours automatically. To increase the period of offline indexing (how far in the past to re-index the logs), see sk111766.
CCSM R77/R80/ELITE