XnView Software

Hello,
Each time I lauch XnView MP it reconstructs the thumbnail database (capture #1)
Whenever I swap to a new pre-recorded disposition, it restart build the DB again (capture #2)
When it's done the size of the db is 0 ! (capture #3)

It was not acting this way at the begining, What is I do wrong? How can I correct this ?

Thank you in advance for your help
François

Environnement : Linux Mint 18.3

Or it has nothing to do with thumbnail database... It seems like when a view is displayed (product launched or disposition change) it starts processing "something" that takes about a minute. Could it be due to the fact all my 6400 pics are in the same folder?