This action cannot be performed outside of opening

I have almost 30 operators in my server.I have given same permissions for each one of them.There is no "opening hours" set for any of the groups.But web app and android behave diffrently for some operators.For some operators when they try to invite visitors to chat from web app / Android app this error pops up -> "This action cannot be performed outside of opening hours". But for rest of the operators it works fine. This issue is not there in desktop app!!.