Match by payroll but employee max out earlier

The plan set up by payroll match, but the employee max out earlier of the year, is that wrong to keep allocation match to employee even though there are no employee contributions in later payrolls? Match is immediately vested and the plan is not a safe harbor plan.

That depends on the plan document. If you have  per payroll match you are violating the terms of the Plan document. If your plan matches on annual compensation or you have a true up you have no problem with what you are doing; I assume you are doing it for all similarly situated employees and not just a specific HCE who maxed out.

Yes, unless the plan also has a true-up provision or otherwise allows calculation on annual basis.