Thanks @maheshdadhich
Yes, you are right.
I do a lots of test and later today I found it out if I fill up that field I can get the correct number of entries.
Actually it's weird because my flow was set and run correctly before.
I guess there may be some updates from Microsoft.
I tested over different file library and found even if I left that field blank, I can get the right no. of entries.
The problem just happens to this particular library.
Further investigation found files created after around July 30 was not listed.
Therefore I guess something changed by Microsoft.
Anyway, glad it's fine now.