What “action” can be taken….?
If you mean some kind of punitive action, then the answer is absolutely nothing
Action in regard to sporadic attendance or action in regard to not sending apologies for sporadic attendance.
In reverse order - what action about not sending apologies…
Is the subject a recently arrived Cllr or long standing?
Have they had an induction process if newly in role (which in our example is a specific responsibility of the clerk)
What is the issue about a Cllr not sending apologies for non-attendance - they are irrelevant other than as a notional courtesy, they are either present at the meeting and recorded as such or they are absent. You literally can do NOTHING about a Cllr not submitting an apology other than ask if they know it is an option
Sporadic attendance at meetings - again, you can ask if there is a reason but it will be entirely at the subjects discretion whether they divulge and - other than 6 months continuous non attendance - there isn’t any ACTION which can be taken
Takes all sorts - maybe 1 in 3 is as much as they can or want to contribute and if that is the case the only action is to say “…thank you, understood, see you next time…” and get on with something else