As tables are used (and get older) the suction from the vacuum inside the table top might gradually decrease.
At some or all vacuum sections, there might be a problem to keep the material in place during cutting or milling.
Check if vacuum is weaker in some sections/areas or all over the table.
Check for PVC cutting underlay that the holes in the table and the underlay match.
Check that there is no air leakage from the vacuum tubes and that the tubes going into the table top are correctly positioned and have not dropped down and started leaking.
Check that the cutting underlay is not filled or clogged with dust from material or is worn out.
Check that the 1 mm vacuum holes in table top are not blocked with dust.
To clean vacuum holes, use vacuum cleaner and visually check to see that holes are open. If not, use pin (a paper clip/a drill bit) and stick open the holes one by one.
When running a job that does not cover all active vacuum zone area, it is recommended to cover unused area.
For Xx tables, there is a vacuum hole cleaner tool kit available.
If material is moving and there is a lot of uncovered active vacuum holes you should cover them. This is mainly a general advice when vacuum is good and material size is small. It can help as a short time workaround if vacuum is low.