Cannot use search fucntion

[omorobot]

I have been using search in confluence so far no problem and all of sudden I see below image when trying to search pages. 

I tried to remove contents in index and journal folder under confluence home directory. and rebuild the search index but did not solve the problem.

What else can I try to solve this issue?

[Nic Brough -Adaptavist-]

What does the log say the problem is?

[omorobot]

which log should I check? 

There are just too many items in the log files.

[omorobot]

2020-12-10 20:31:58,945 INFO [Caesium-1-3] [atlassian.crowd.directory.DbCachingRemoteDirectory] synchroniseCache INCREMENTAL synchronisation complete for directory [ 34144257 ] in [ 62ms ]

This is what just added after trying to search with keyword.

[Nic Brough -Adaptavist-]

The application log should be <confluence home directory>/log/atlassian-confluence.log

I would not expect search errors to be logged anywhere else, despite the piles of disparate logs the app seems to want to create