I tried with different moods. I don't know what was the problem. I made a new game and it worked fine (without the creativity maxed out but I doubt that was the problem). In the end I decided to use cheats described here so I can get pasts the milestones in that creativity aspiration which had two tasks with the activity table.
I still don't know what was the problem and I forgot to debug that object with shift click. The activity table doesn't work still like it's supposed to.
This was the first time I used cheats but as far as I can see on the PCs there are no trophies which you may lose like on consoles.
Product: The Sims 4
Platform:PC
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What is your current game version number? 1.70.84.1020
What expansions, game packs, and stuff packs do you have installed? Get To Work, Dine Out and Nifty Knitting
Steps: How can we find the bug ourselves? Bring child sim to activity table to draw while inspired
What happens when the bug occurs? The green progress meter doesn't move while drawing at the activity table, to complete the Artistic Prodigy (Childhood Aspiration)
What do you expect to see? The sim to complete the drawing, the green progress meter to finish and for the sim to be able fulfil the Artistic Prodigy aspiration.
Have you installed any customization with the game, e.g. Custom Content or Mods? Never used.
Did this issue appear after a specific patch or change you made to your system? No
I've tried on two different households. With both kids they were inspired and the green progress meter didn't move.
Edit By Crinrict: Adjusted Title
