The problem started today without any updates or modifications, however the Off-Canvas panel button became unresponsive. I can safely assume that it's script conflict related but I'm way to much of a script novice to find the source of the potential conflict. I have disabled the feature for now as it's affecting a live site, but pending a response here I will activate the usual JS account with updated details included.

I look forward in anticipation of resolving this issue as soon as possible.

Hi,

the issue because this css

.collapse {
  position: relative;
}

.t3-navbar.navbar-collapse.collapse {
  position: inherit;
}

Thank you Albertus, Your suggestion worked a treat although I am curious to know how the existing custom.css suddenly disappeared. Never mind eh! Solved. Thanks.