I really liked Happy Death Day (2017). Happy Death Day 2U (Blu-ray release 2019-5-14) continues the story and turns it into a sci-fi comedy. It turns out that the time loop was caused by a science experiment, and it even transports the protagonist into a parallel universe where her mother is still alive, but her boyfriend is with somebody else.
Although the sequel retains the slasher element in a few parts of the movie, it no longer generates the tension required, and there is no mystery solving because it is fairly obvious. I like this sequel too and appreciate its attempt to not simply repeat the same formula, but I can also understand it is no longer a slasher movie that people want to see, accounting for the lower box office.