I suggest that you try the following to diagnose the problem:
Place your film into a glass carrier. If you don’t have a glass carrier, get two identical pieces of window glass cut to the size of the carrier, de-burr the edges with a fine whetstone to prevent scratching the negative, place the negative into the temporary carrier (the glass must be perfectly clean) tape the edges with black tape to prevent light spill.
Put the negative in the glass carrier or temporary glass carrier into the enlarger. Raise the head all the way up, focus carefully on the grain, and make a print—even a small one will suffice—at the optimum aperture of f/11 (for an f/5.6 lens) Critically evaluate the fine detail and contrast of the print. The negative was held flat between the two sheets of glass so it can’t “pop”.
Make certain that the timer isn’t somewhere where the force of triggering it can start the column vibrating.
Any lack of sharpness must be due to the lens, focus error, or vibration or movement of the enlarger during the exposure. If you prevent vibration and you’re certain that the grain focus was perfect, then what you see in the print should be strictly due to the lens and the image quality of the negative.
If the bottom surface of the upper glass isn’t anti-Newton you might see Newton rings on the print, but that won’t prevent evaluating the projection quality of the lens.