Excuse me if I am barking up the wrong tree, but.
If your enlarger is of the cold cathode type, then it is very necessary to allow the system to warm up before use.

Average time about 1/2 hour. Even so the light level will increase as the tube gets hotter. Any enlarging done while the tube is not hot enough, will result in considerable difference when the tube is hot and at working temp.

In such cases, exposure adjustments are necessary to ensure that the first set of prints do not vary in density to those made last....