Domain mapping on a multisite installation

Hi,

I have been using Download Monitor for quite a while and appreciate it mluch.

But today, just before delivering a website to my client occurs a problem : I use the plugin on a child domain of a wordpress multisite and have a dommain mapping. When I set up this new domain as the primary domain, all downloads fail (ERR_INVALID_RESPONSE).
How can I solve this issue ?
Thanks

https://wordpress.org/plugins/download-monitor/