Can't resolve dependencies: soapui-maven-plugin:5.3.0

Since a couple of days we cannot download the soapui-maven-plugin:

Failed to retrieve plugin descriptor for com.smartbear.soapui:soapui-maven-plugin:5.3.0: Plugin com.smartbear.soapui:soapui-maven-plugin:5.3.0 or one of its dependencies could not be resolved: Failed to read artifact descriptor for com.smartbear.soapui:soapui-maven-plugin:jar:5.3.0

When i go to 'https://rapi.tools.ops.smartbear.io/nexus/content/groups/public/com/smartbear/soapui/soapui-maven-plugin/' i get a http 504 Gateway time-out.

It seems that Smartbear artifacts are not availale.