WPFC: Activation aborted and now htaccess is being deleted

Hello,

I have an urgent issue regarding WP Fastest Cache.
The activation of the plugin on my WP 6.0.3 site aborted because it said the htacess could not be written.
So decided to remove the plugin completely, but my .htaccess file gets deleted again and again.
Even if I restore the file manually via SFTP or automatically by changing the permalinks (which triggers WP to write the htaccess again), the .htaccess file is being deleted after a few minutes. Instead an htaccess.ui file is there with minimum content:

AddHandler x-mapp-php5.5 .php

I couldn’t find anything of a file named htaccess.ui
Could it be that the uninstallation was not successful?

Thanks in advance!