I've had this happen to me with the child skills. New Skill Day happened to pop up on one of my skill-building days, but neither of my twins got the tradition fulfilled as they ranked up in child skills. However, when they leveled an adult skill they unlocked (by hitting level 10 in a skill), it counted.
Wanted to chime in that since the beginning, this has been happening to me too. From my experience, the "improve an existing skill" is what won't register.
@apincasIt says New skill day or existing skills. I don't think EA has all the skills updated on it to trigger it.
I completed the Research & Debate skill from DU and that did not trigger the tradition. I also completed a base game skill and that didn't trigger the tradition.
So both base game expanded skills don't trigger it.
What level was the skill you were trying to improve? I know in the past this only work for low or skills that were lower levels (ie 5 or lower). When I do skills that are below level 4 and raise it a level it will complete the tradition for me.
Product: The Sims 4
Which language are you playing the game in? English
How often does the bug occur? Occasionally (10% - 49%)
What is your current game version number? 188.8.131.520
What expansions, game packs, and stuff packs do you have installed? City Living, Discover University, Get to Work, Island Living, Seasons, Dine Out, Parenthood, Spa Day, Cool Kitchen Stuff, Fitness Stuff, Laundry Day Stuff, Moschino Stuff, Perfect Patio Stuff, Romantic Garden Stuff, Vintage Glamour Stuff
Steps: How can we find the bug ourselves? Have level 9 Research and Debate skill, and wait for New Skill Day to occur. Then, use a computer to write a research paper to reach level 10 Research and Debate
What happens when the bug occurs? The "learn new skill" tradition on New Skill Day is not completed by reaching level 10 Research and Debate
What do you expect to see? Reaching level 10 Research and Debate should count for tradition completion on New Skill Day
Have you installed any customization with the game, e.g. Custom Content or Mods? Not now. I've removed them.
Did this issue appear after a specific patch or change you made to your system? Neutral/Not Sure