I opened Renshuu this morning as I do every day, but I discovered that my cards had not refreshed for the new day. This means I have no reviews or new cards to study. It is even stranger that all of my masteries failed to update with the exception of one, which appears to have refreshed as expected.
I have just realized that I can force a refresh by going into each mastery section and clicking the Study button. This is less urgent now because I am at least able to complete my reviews, but I believe this issue is significant enough to warrant further investigation.
