The Charles SSL/HTTPS proxying was working fine on my Samsung Galaxy S5 phone.
I remove the certificate while not debugging because the phone warns me about the connection being monitored by a third party.
Now when I attempt to re-download the certificate from http://www.charlesproxy.com/getssl/ I get a charles-proxy-ssl-proxying-certificate.pem download failed due to network failures error:
The phone is set up to use the Charles proxy. HTTP traffic can be inspected in Charles.
I'm running Charles 3.11.4 but I've also tested with 3.11.2. The phone is running Android 5.0
I tested with an LG Nexus 5 and the certificate downloaded and installed without any problems.
As a workaround, type this into your address bar and press Go.
data:text/html,<a href=http://www.charlesproxy.com/getssl/>Save This Link
Long-press on the link that appears and choose Save Link. Then open the certificate you downloaded.