Flac disappear in Musicbee collection

[Carmilien]

Hello,
I have a problem with my Musicbee collections. I use Musicbee portable from my NAS where my music files are also.
I created 3 folders on my NAS, "Musicbee" which contains the portable version of Musicbee that I run from either of my 2 pcs, "Music" which contains Flac files and "MP3".
When I create a collection including the 2 music folders, Musicbee scans the 2 folders and finds all the files and reads them without any problem.
But when I close Musicbee and reopen it, after a few seconds it opens a window telling me "these files are no longer in the intended location, should they be removed from the collection?"
If I answer YES, he removes all the Flac from the collection. If I answer NO, it puts an exclamation mark in front of the concerned tracks in the playlist and does not read them when I click on them.

Do you have any idea where my problem might come from?
Thank you in advance for your help.

[Carmilien]

To test, I copied and pasted my Musicbee, Flac and Mp3 folders on a usb disk on one of my pcs, recreated a collection pointing to the 2 folders Flac and Mp3. Same problem after reboot, Musicbee tells me that the Flac are no longer in the indicated location and wants to remove them from the collection...
I am using version 3.2.6827