Terms selection

Hi – I love this plugin and have used it on several sites. Today I went into a site I built a year or two ago – it’s having a total rebuild. It has UTC version 2.6.1 – but I can’t get my list of tags in ‘terms’ to ‘take’. I’m listing them with a comma between but as soon as I save they disappear. I seem to recollect a tick list appearing when I last used the plugin. Am I missing something obvious?
Many thanks
Jan

https://www.ads-software.com/plugins/ultimate-tag-cloud-widget/