Hierarchy slicer was working fine till yesterday and when I opened today in Power BI service it's not working as expected. But it is working fine in power BI desktop version.
Here is the desktop version and power BI service version(msit.powerbi.com)
Based on my test using Chrome and Edge, I cannot produce your issue here.
1. Which browser did you use? Could you please try to clean the cach and try again?
2. If the issue still occur, kind share your pbix to me, so that I can try again by my side.
Even we are facing the same issue in all of our published reports to the powerbi service having Hierarchy Slicer plotted on the reports.
Already raised support ticket for the same.
Has your issue been solved? If so, kindly mark my answer as a solution to close the case. If any other question, feel free to let me know please.