Data deleted by Nextcloud client

Nextcloud Desktop Client Version: 3.7.3
Operating system and version: Windows 10.0.19044
Apache or nginx version (eg, Apache 2.4.25): n/a
PHP version (eg, 7.4): n/a

Dear all,
yesterday, I have installed the Nextcloud Desktop Client on my computer in order to save some folders on my hard drive to the cloud.
After installlation (during which I have selected “keep local folders”), I had selected a folder that contains quite a number of subfolders, which were also all selected. During the upload process, I received a message from the client saying that the data I want to upload exceeds the available cloud space. I then deselected some of the subfolders (being confident that this means "do exempt this folder from syncing) and continued the sync process.
What happened, however, is that all the now deselected folders that haven’t been uploaded to the cloud were deleted from my hard drive. The client still shows the original folder structure and once I reselect a folder, the client would recreate it - but the files are all gone…
I have already had contact with the organisation hosting the cloud but their backups do seem to contain only a small portion of the missing files. What also troubles me is the fact that a recovers programme (Recuva) is not able to detect any of the deleted files on my hard drive.
I would be very glad if anone can show me a way to get these files back!
I also have the logfiles, but do not know how to open them in order for you to replicate what has gone wrong.

Is this the first time you’ve seen this error? : Y

Steps to replicate it: none

The output of your Nextcloud log in Admin > Logging:

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The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

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The output of your Apache/nginx/system log in /var/log/____:

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Output errors in nextcloud.log in /var/www/ or as admin user in top right menu, filtering for errors. Use a pastebin service if necessary.

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