Do you mean in the weir box that is inside the tank, or the outer box?
If it's too low in the weir box, and bubbles are getting in and breaking siphon, this is not good.
A Utube should be almost entirely full, like this

Post a pic, some overflows are fine with low water as long as siphon is maintained, and the main tank and the sump remain stable.
If siphon is breaking, then there is a problem.
Also water level in an overflow can be adjusted by moving the inside plumbing height, unless it is glued in position.
notice the low water level in the left part of this CPR overfow box, this is normal

now notice the level in this box, also normal
