I just wanted to let everyone know that Memrise can reinstate your lost streak if it has reset on its own.
I contacted support and told them that my running streak I had just disappeared and it has done it a few times. I never changed time zones or anything either.
Support was able to reinstate my streak with no issues. So if you too have this problem, just send them an email via: http://www.memrise.com/contact/ and they can redo it for you also. I sent my message under Support Request.
However, I still have an issue that my 30 day badge was not given nor was my Best Streak updated. Support didn’t have any help for those two issues. 