I notice a bug/problem by using Let's Encrypt Plugin for the address used to acces the i-mscp dashboard. I will explain the whole scenario,
We have an i-mscp (1.5.1) instance with Let's Encrypt (3.3.0) plugin.
The i-mscp dashboard is access on, let's say, https://i-mscp.domain.tld.
If you enter http://i-mscp.domain.tld (without SSL) in a browser, the first added domain web site is displayed.
If you disabled that first added domain account, aparently the renewal of the Let's Encrypt certificate for the control pannel and services can't be done.
If I enable that first added domain an push the renew button, all works OK.
See attachement for details.
If you need more info, please let me know.