When opening a file within the "Files" plugin in Roundcube, I get the following error in the console:

Failed to load resource: the server responded with a status of 404 (Not Found)
https://webmail.xxx.eu/assets/program/resources/blank.tiff

In seems to come from /usr/share/chwala/public_html/js/files_api.js (line 566):

img.src = this.env.resources_dir + '/blank.tiff';

I think, it should be:

img.src = this.env.resources_dir + '/blank.tif';

After the change, Chrome did not complain any more.

My chwala version: chwala-0.5-12.1.el7.kolab_16.noarch
I don't know exactly whether this is a chwala issue, so please let me know, if you need the version of some other package.