It would be lovely to live in a world where parish councils function as efficient beacons of local democracy, with fastidious clerks providing immaculate and timely paperwork. Sadly, the real world ain't like that and we hear so many horror stories.
My advice to you is to explore training opportunities for your Chair, your Clerk and all members of the council, to help them to understand their roles and responsibilities. Your local association should be able to provide this. Give everybody a copy of the Good Councillors Guide 2018, which contains so much useful information. If you have a competent neighbouring council, suggest that members attend one of their meetings to see how they conduct themselves. Attendance rates can usually be improved by publishing the attendance record for each councillor at the end of the year and reminding members of Section 85, the six-month rule.
It sounds as though there is an issue with your Clerk and you haven't commented on their experience/qualifications etc. Has anybody sat down with the Clerk to ascertain why they have been unable to meet deadlines etc? The council, as the employer, has a duty of care and should be working in a positive and supportive manner to help the employee.
If there is nothing new to say about the long-standing agenda items, they shouldn't be on the agenda. Confidential business items are for commercially sensitive matters, so the same topic of discussion can be open at one meeting, then confidential at the next, according to the matters to be discussed.
I hope this is helpful.