I agree, but the keyword here is "should". There are many reasons or circumstances for a delay in publishing an agenda. Firstly, if it happens repeatedly, it's a problem that must be addressed. If it's a ploy to reduce public involvement, that is unacceptable. But if the Clerk is unwell and unable to pin the agenda on the notice board, there might be a delay. In a previous role, I had a large noticeboard in an exposed location and it was unsafe for me to open it in windy conditions.
Cancelling the meeting and rearranging can be complicated, as the dates are set for a whole year. We struggle to book meeting space in busy community centres and need to coordinate diaries with our district and county councillors, who attend our meetings. Planning response deadlines or other consultations may be missed through the cancellation of a meeting. A delay in publishing on a website is harder to justify.
This is a key responsibility for clerks and one that must be taken seriously.