I have this problem now as well,
i did not have any issues before the april 16 patch. I tend to do alot of writing. I had 2 sims just a few days ago (real life time) writing all kinds of books including fantasy.(this was a new game as well started less than 1 week ago). I had the all expansions for this save.
last 2 days i started a new game. Sim just hit leave 7 writing and fantasy books become available. I finished lvl 10 gardening career earlier today and did some writing of books for research, grants, and the other few options for writing books for fame. i created 2 normal books i think 1 children's and maybe a non fiction not sure. I started a freelance writer career, first assignment was create a motivational book (no issues here). 2nd assignment create a fantasy book, started it no issues. then stopped to sleep in game. next day was blizzard (not sure if matters) went to resume fantasy book and I have same issue. Sim sits down, looks like its going to start writing then just gets up out of chair many times. will not resume writing.
I never have had this issue before and everyone of my sims always invest alot of time in writing books including all types many of each. I never had expansions except the get to work one. I just purchased all the other expansions less than 1 week ago during origin sale.
hope this helps,
Rhah