Dealt with this all my life and helped many skaters thru it.
The clinic most likely put you into a stance you are not normally in ie a little deeper in your stance. This extra pressure could have been the trigger point that caused your lace bite to elevate itself to a noticeable point. Lace bite generally doesn't happen immediately, it's micro trauma happening on the tendon and in between skates your body is trying to heal it. Time on ice, pressure on tendon, age, recovery capability are just some of the factors that determine how you get it and react to it.
If you are getting it during the class it tells me that you are borderline lacebite the rest of the time ie enough pressure to have it happening but your body is just managing to keep it under control.
How to fix it:- Bottom line is you have to get the pressure OFF the tendon, this is the most important thing to do for your long term skating health. Lacebite pads, unless they have a channel cut in them for the tendon to sit in, are a waste of time. The options I know that work are: 1: Option B laces. 2: Forsberg pads, downside is you have to tape them to the front of your ankle every time you skate. Make your own from 1/2" pipe insulation. 3: Boots that have enough volume. 4: A new tongue may help if it increases the volume in the boot (ie a thinner tongue) or if the tongue has broken down. 5: Drop eyelets or skate with laces untied 6: Eyelet extenders.
the last option is the one I recommend to skaters, it is cheap, effective and you can use them on any skate. Now you can choose the skate that fit you the best everywhere else (retail skates) and then fix any volume issue.: