Have you tried clearing your cookies? That's what Jamie suggested in another thread (https://www.wikitree.com/g2g/1150583/is-anyone-having-trouble-logging-in-to-rootsearch?show=1152347#c1152347) and that's what fixed it for me, but I gather it doesn't work for everybody.
Where it asks for "API: clientLogin" just enter the same email address and password that you use to login to WikiTree. The first time after you login it will then ask for the Profile ID you want to use RootsSearch for, but after that first time it picks up the details automatically like it used to.
It might be worth you adding a comment to https://www.wikitree.com/g2g/1152340/log-in-to-rootssearch-app, including what type of device you are having the problem on (laptop, iPhone or whatever), as Jamie seems to be watching that thread and might be able to offer some advice.
Enter a WikiTree ID to research with RootsSearch. Read the WikiTree article for more information.
Profile Id: Load